Yes, it definitely does get easier as your hair gets longer.
As far as technique - practice! play! That's how I learned how to do my hair (and I still can't pull off a cornrow I'm willing to walk out of the house with). Sometimes, I'll just spend an hour or two in the bathroom, messing around with my head, doing and redoing styles until I can get them just so.
I know what you mean about your hair being shorter on one side of your head - the left side of my head is about 2-3 inches shorter than everywhere else, because the hair over there is 4b, and it + dye + bleach = breakage! I learned to 'favor' that side of my head. So - for example, when I am doing twists across my head - I always start them on the right side, so that by the time I get to the shorter left side, I'm finishing up the twist, and the shortness doesn't matter as much. Also - if I'm doing some sort of 'out' part in the front, I'll be sure to put the part MUCH closer to the left side than to the right, so that the fact that my hair is much shorter doesn't stand out as much.
Two things to remember -
1) the smaller/skinner the twists/flattwists/cornrows are, the less length you need to pull off the style.
2) If you have any sort of shrinkage, banding/stretching out your hair (get it wet, comb it out, put it is as few twists as you can pull off - and they don't have to be cute) let it dry, then comb it out again dry with a little conditioner/hairbutter on it - it'll allow you to have the most length possible to work with.
As far as parting goes - if you hair is damp/oiled/buttery, parting goes SOOO much easier. Also, the narrower your comb is, the better. I part with a rattail comb - it doesn't get anywhere NEAR combing my hair, but the thinness of the comb makes for neater parts. Also - ya need TWO mirrors. I'm blessed to have a built in 3-way mirror in my bathroom, and I can't imagine parting without two mirrors (at least) so that you can see what you are doing. You might also want to try 'feeling' out your parts - then I'm two strand twisting my hair, I jsut get a rough 'idea' of where the parts are - perfection isn't crucial...
SHeeesshh!! I ain't mean to write a dang book - I hope some of that helps DDtexlaxd....