One thing I learned a long time ago is to not make things too complex. There have been MANY good suggestions and comments in this thread. Here's what I have found in drumming (and teach), and have applied it successfully in many other areas (whistles, etc.,)
Start slowly and be precise.
Make sure every move is spot on perfect.
Have NO excess movement at ALL. No extra flourishes, keep fingers down as close to the instument strings, holes, whatever, as you possibly can.
RELAX anything that is touching your instrument, or that is connected to something touching the instrument or that is connected to something connected to something touching the instrument (you get the idea...)
Get a good, digital metronome, play with and pay attention to it - it won't vary, you might. When you have the rythm dead on, pick the pace up. Continue to pick the pace up until you reach the tempo you want.
When you get to tempo, don't be surprised if you find yourself with PILES of time between notes - because you have reduced everything to get to the speed you want - which will give you plenty of time to get the things you WANT in (dynamics, "warmth", etc.,) where you want them.
Off to work.