Here are a few thoughts. Speed should be relative. That is to say, you only have to be faster than the opponent. While optimizing your own speed is a worthy goal, it is more important to know how to rob the opponent of speed. The main ways are
You must also choose techniques that fit you. Someone who is very tall will probably waste their time practicing stomach shots, while a shorter person should concentrate on these. Yes there are cases where the tall person might need to do such a technique, but the probability is lower. Marc MacYoung's admonition to "train for probabilities, not possibilities" is correct.
Position and angle come from body movement (taisabaki) drills. In particular, footwork drills.
Smoothness is what I'm going to chat about now. You should practice techniques at first as slowly as you can and still have the technique work. This will let you understand what the technique does, but more importantly, being able to do something right means you can do it faster rather than being fast and sloppy, which just means that all you can do is hope it works. My model for this, by the way, is a discipline that requires accuracy to the quarter inch and timing to the hundredth of a second: music.
In music – and it is really hard to improve on this – what you do is get the passage perfect at
a slow tempo. Then you increase the speed slightly. Once you have the passage at about 75% as fast
as you like, you vary the rhythm by making pairs of notes faster. You vary which notes. What this
does is allow you to practice positioning for the next movement. Stated differently, to speed it
up, remove the spaces between things you want to do. Graphically, if you start with
all even notes like
| | | | | | | | | | X X X X X X X X X X
| | | | | | X X X X X X X X X Q Q S Q Q S Q Q Sor maybe as
| | | | | | X X X X X X X X S Q Q S S Q Q Sor with dotted rythms like
| | | | | X XX XX XX XXand finally reverse dotting (Hungarian rhythm)
| | | | | XX XX XX XX XXNotice that the faster pairs are played at 150% speed – far faster than your goal. Then when this is easy, up the speed and try it faster until you reach your goal.
Once you feel pretty comfortable with it, try playing the passage up to 125% speed. Then play it at 50% speed. If feels pretty much the same (so no hiccups where you stumble) then you are doing it right. You know that you have this down really well when you find that playing the passage works best the first few times rather than with extended practice.
A lot of training routines rely on rhythm. This is a good idea, and what I have outlined is a simple but pretty effective way to train. A steady beat (like a metronome) is fine and you can also do this to music. If you do it with music, don't get carried away and dance. Many people do and sell it as exercise (boxercise, taebo and such) but that will ruin your trainig.
Of course, this would be different if we were, say, arthropods (like spiders) which have an exoskeleton and only flexors (to pull in legs), but no extensors. To extend their legs, they have a hydraulic system that forces blood into the limbs. This actually works better than our poor system and is the reason that a spider can jump up to 25 times its own body length. This is why arthropods curl up when they die; there is no more blood pressure to keep the legs extended. But I digress, and rather weirdly at that...
At the physiological level, it has been shown that firing nerves in repeated patterns causes them to grow larger and fire more easily subsequently. This is the mechanism by which you learn a new reflex, be it playing a C major chord or firing a punch. This allows for larger syntactical units of motion to be done. Progress is measured by what we can do automatically. At his or her best, a musician can improvise astonishingly complex music. Being able to do this myself, what occurs is that one has the patterns so well ingrained that only qualitative control needs to be exercised and asserting conscious control is the exception. Of course, the flip side of that is if you practice something wrong up to the level of an automatic behavior it can be rather frustrating to say the least.