I was in the same boat, I played for about 7 years then quit for 15 :P I just picked it up again about 2 months ago and I'm better in many ways than I was before I stopped playing.
I try to divide my practice time into 4 areas:
- Warmup - usually involves practicing to a metronome and running scales up and down the neck. First linearly, then using intervals, maybe 3rds. Playing 8th, 16th notes and then double,triplets and etc and finally I finish with some neat exercises I picked up from:
YouTube - ‪JOHN PATITUCCI Bass Workshop 1 3 Left Hand Dexterity Builders chunk 1‬‏
- Technique/Sight reading - I find something that's right on the border of my abilities to play and I work on it until I get it down cold. I just did the head to Donna Lee and now for instance I'm working on this:
http://www.lucaspickford.com/raju.jpg it's a bitch to play at tempo but doing this has really helped expand my technique very quickly, l'm almost back to where I was when I quit after not playing for many years. Alot has to do with muscle memory but challenging yourself is also important.
- Theory/Harmony - Tons of resources on the web for this. I just pick something and work on it. Here's a good place to start under "lessons"
Pick's Place-www.lucaspickford.com
- Playing - I have about 75+ Jamey Aebersold recordings to practice with.
Jamey Aebersold Jazz
If you just try and be disciplined and stick to it you'll break out of your rut.
I keep it simple, I practice things over and over until they're burned into my head. When I was learning the head to Donna Lee I practiced it so much that my wife finally got sick of it and stormed out of the living room, she's a patient woman, lol this went on for over a week straight for hours a day.