Bart has a short article up on
The Fine Art of Practice that's a good start.
outside of telling you what i do, [stretch 10 minutes, hands 15 minutes, rudiment rundown 5 minutes, free-form play 10 minutes, exercises my teachers give me 2 hours, free-form play 15 minutes, rest, band stuff 20 minutes, rest... repeat, depending on how much time i have], this area here:
A lot of the time I practice little things here and there
makes me think this is what's tripping you up. i may be reading into it, but it sounds like you are noodling... playing with a little bit of this and a little bit of that, with no real focus.
rather than lay out a whole bunch of things you want to get better at, lay out 2 or 3 things you want to focus on. it could be your timekeeping, a certain groove, a particular sticking combination, a double bass pattern... whatever.
stick to those things and make a focused effort practicing them, whether you spend 20 minutes on one thing or 2 hours.
when you feel you've made some progress [and it may not happen right away], see if you can chain the things you've practiced together and make some music out of it. this will help you see what you've learned, put it in context, and see how well you 'own' it.
again, things take time...
regarding your other question about maintaining what you've learned while learning new stuff:
you're going to reach a point where you will be able to do certain things very well. that's just a fact. if you keep repeating something, it will become second nature.so don't kill yourself practicing that all over again if you already know it and do it well. think about taking the new stuff you learn and putting it in the context of the old stuff you know instead. because you're probably not going to forget much -- especially if you're young! and if you do, you'll just need a quick refresher.
in general, i think it's good to do a 'holistic' practice -- work on hands, grooves, overall technique, stickings, songs, etc. but i think you have to make each of those areas a focused practice, and make some gains in each area. the areas that you don't make headway in are the ones you have to go back to.
the other thing i think is important is to take rests during practice. you get to points of diminished return, where more practice doesn't serve a purpose. know when to chill and give you brain and body time to absorb everything. i used to go through long stretches of intense practice. sometimes it worked, but lots of times i wound up totally shot or worse, injured.
good luck, and when you get those double bass chops happenin', gimme a shout. i want to learn that!
