Let me divide speed playing into two categories: composed and improvised. The composed category includes everything where what to be played has been worked out ahead of time. The improvised category includes everything else, where what is played was not planned ahead of time.
To play something that has been already defined--there's no getting around it, you have to play it that way (or some planned variant of that way). You have to work with your skill at the elements required for the phrases you are going to play.
Sometimes there will be certain elements: note transitions or jumps or technical difficulties that are particularly difficult to play. As you practice you will become aware of the places you have the most difficulty. These are the areas to isolate and work on individually. Practice those elements enough that you gain control of them. Practice them enough that instead of dreading them, you look forward to them because you can do them so well. Practice them enough that other elements of the music become more difficult than these, which were more difficult at first. Gaining control of these new problem elements will probably be far easier than controlling the initial elements. Keep playing the initial difficult but now not problematic elements as you practice the new less difficult but more problematic ones. This should become a process of smoothing and controlling the transitions between the different elements of the phrase(s).
Investigation of the underlying breathing patterns required to play the notes in the phrase can help in determining what you need to do to be able to execute the passage properly. Memory becomes a dominant factor when playing fast composed passages, because speed means lots of notes and rhythmic patterns, and lots of anything means lots to remember. Understanding the underlying breathing patterns gives you something besides individual notes to remember and on which to focus, making the memory task easier, as well as enhancing the ability to execute the phrase.
When you eventually move to faster speeds, you cut back on these exaggerated movements which tends to keep the note transition relative-timings fairly consistent. For example, if you are playing slowly and still require some extremely fast compact movement to play some sequence of notes, there's no room there to speed up that part later. You need to put some exaggerated smooth and appropriate motions in your play so you know you are practicing at a speed that you will be able to improve upon later. Some parts may require more exaggerated movements than others to keep the tempo and rhythm correct. Where you are least able to exaggerate the slowness is where you will be limited on how fast you can play the passage.
Practice playing very smoothly at very slow speeds initially. Only after you get comfortable and competent playing at slow speeds should you move to faster speeds. As you start to speed things up, intermix the faster passage with the slower one in a controlled way, as a whole--don't play a little fast and a little slow during the passage. Keep the passage smooth and in rhythm in its entirety, but play the different speed passages back to back. For example, play the passage at the speed you are comfortable with, then push yourself a little faster for the whole passage and don't worry about missing notes. Keep going and keep the rhythmic integrity intact. Keep your dynamics and phrasing under control, and if you hit some wrong notes.. so be it, that's okay. Then go back and play the passage at the slower speed at which you can hit all the notes comfortably with exaggerated control. If you find you can't keep the rhythmic integrity and dynamics in place, you aren't ready to move to a higher speed. Concentrate on those musical elements at the slower speed and get them ingrained in your aural image of the passage.
Think about relaxing, and minimizing the muscles involved in playing the passage (though the ones in action may be making extended movements). As you play slowly, work on optimizing your approach to the passage, playing smoothly and efficiently, but with a degree of motion commensurate with the speed at which you are playing.
Start with only a couple of notes, and gradually add one before or one after the small set you are working on. Slowly build up the number of notes you are playing and build up the context of the fast passages, the notes leading into the passage, the passage itself, and the notes following the passage.
For example, you could ornament a long held 3 draw note with a quick shake to the 4 draw and back. You could ornament a long 4 draw with a succession of 3 draw to 4 draw shakes. You could ornament the 3 draw of the shake with a 1/2 step bend. You could ornament back to back 6 draws with an evenly spaced 4-5-4 shake in between. In other words, the number of possible ornamentations is vast!
Ornamentation is taking advantage of the musical space provided by held notes and rests in the musical phrase to add notes in the rhythmic context of the underlying music.
Ornamentation should work with the flow of the music and the flow into, during, and out of a phrase.
The above principles make it clear that ornamentation is more concerned with rhythm and feel than with the exact notes to be played. These notes are short, being played quickly, and lose some of their musical significance They are ornaments, not the tree or its branches. Instead of thinking notes, ornamentation is more concerned with direction--where direction means moving toward a note, staying on the note, or moving away from a note. Or some combination of those motions. You can start with your primary note and stay there; or play notes that move ever farther away from it; or first move away from it, then back to it; or jump away from it and move steadily back to it. Or even combinations of those, changing directions more than once before returning to the primary note.
Where do you get the primary note? You either have it already because you're ornamenting a preset phrase, lick or riff, or you pick it.
Primary notes are most often picked from the scale and mode of the music, e.g. C major or D minor or E blues. The Layout Generator can show you the notes in the scale and mode of the music for different positions.
Primary notes are most (or very) often picked from the notes in the current chordal harmony, even if that harmony contains notes not part of the basic scale.
Improvisation about a melody often will involving picking primary notes from that melody at the time the melody note would or does occur. Improvisation about a melody will often use rhythmic patterns from that melody with different notes, and improvisation of primary notes will often be driven by the underlying rhythmic pattern, whether it comes from a fore-known phrase or not.
One benefit to the use of breathing patterns is realized by selecting rhythmic patterns with breathe-in-breathe-out symmetry so that long lines can be played without running out of breath, in either direction.
In other words, a certain number of beats or bars can be allocated for speed work. Many different notes and different rhythmic patterns are used during the fast play. As part of those notes and rhythms, a higher level phrase can be superimposed to emphasize the overall musical rhythm and provide a motivated musical flow through the many short notes.
In still other words, there will be a few important musically motivated notes, and a lot of relatively unimportant notes, which are musically okay as long as they are played at the right time.
These motivated note phrases generate their own breathing patterns. Ornamentation or other quick notes can be chosen that fit with these motivated breathing patterns. This leads to fast lines that fit well with the music, the motivated phrase leading the ear through the flurry of short notes, and are relatively easy to execute since they fall naturally within the breathing patterns generated by the motivated primary note phrases.
These motivated note phrases can be treated as composed, with the fast notes added in an improvised fashion each time. This allows an improvised section of music to be played with consistent feel, if not consistent notes, and is much easier to remember than long lines of short notes played in a particular way. This can lead to music that contains elements of a composed improvisation.
While you're practicing panting, you might as well be playing chords too. Put a low key harp in your mouth and cover a chord and practice your panting so that you get the deepest, biggest, fullest chord you can. Open up your mouth and throat and hide your tongue down at the bottom of your mouth, a soldier hiding from enemy fire. Visualize an egg in there, a large egg pushing the insides of your mouth outward and your tongue down. Pant through the harp, but listen to your chords. Make them sound good. Slow down a little if you have to. Make sure all the notes sound, each one, and try to get them all sounding even. Shift to a double stroke roll--two pulses out and two pulses in. Control the pulses with your diaphragm. Slow down if you have to. Keep it going. Turn it into a train if you want. Say "hooka" when you breathe out and "tooka" when you breathe in. Say "Tah hooka tooka hooka", with "hooka" said while breathing out, and "ta" and "tooka" said breathing in. Move the "Tah" around. Then stop articulating with your tongue--stop saying tah hooka tooka. Open your mouth back up, drop your tongue back down and just play a double stroke roll with big full chords. Keep it under control.
Don't pant for too long or you might get dizzy.
Speed Is It's Own Articulation. Fleeting notes don't require the same degree of control over attack, shaping, and vibrato as slower ones. When you practice by playing fast passages slowly, take care to play with the same playing pressure, legato, staccato or other effects as you will when you finally play them fast. Don't try to enunciate each note in a very fast passage with articulations like Ta, Ha, Da, Ka, etc. Unless you're very practiced with triple-tonguing techniques and synchronizing your tongue with rapid-fire notes, you're probably better off getting your tongue out of the way. Establish a playing pressure, and be able to achieve that pressure for rapid changes in breath direction.. in other words, make sure your pressure is consistent enough that you achieve the same volume inhaling and exhaling--or whatever volume is needed at the time to express the musical dynamics.
Speed can be over used. The harp is best at shaping notes, that is its strength. Speed can add spice to the musical mix, but like cooking with spice, enough is good and too much is worse than none.