It's hard enough to find the time to get behind the kit so when you do, make sure you spend your time wisely; here are a few points to get you going.
Make the most of your time
First of all try and schedule practice time into your working week.
Set a practice routine and stick to it.
A little and often is often the best way to achieve consistency.
Make a list of areas of weakness' you wish to improve upon.
Keep a practice diary so you can see how you are progressing.
Practice with a metronome as much as possible.
Set goals for each practice session or have weekly/monthly aims.
Have a list of songs that you want to be able to play to and work these into your practice routine.
Play to music you wouldn't normally listen to for inspiration and to push you out of your comfort zone.
Find time to video or record yourself playing, then self analyse.
Set up a mirror to check posture and technique
Keep a practice pad next to the sofa and practice while watching TV/in advert breaks.
Go to gigs, any gig. Even if it's a style of music you're not into.
Go to jam nights, playing with other musicians is such an important thing to do.
Study other drummers, either online or even better in person! Use your eyes as well as ears!
Books and other material that I recommend:
The New Breed by Gary Chester
Stick Control by George Lawrence Stone
The All-American Drummer by Charley Wilcoxon
Mind Over Meter by James Hester
The Encyclopedia Of Double Bass Drumming by Bobby Rondinelli
Rockschool Grade books
Go through the Rudiments. You can find these on the Vic Firth website.
Old drum heads
Have a stack of old drum heads that you no longer need? Instead of binning them try a few of these ideas:
You can cut the hoop off and put them on your existing snare head to create a deeper, fatter and darker sound. Experiment with different thicknesses for different sounds.
Or cut them into o-rings which will give a similar but less drastic influence on the sound. These can be used for cutting down overtones on toms too.