There are a few ways to approach climbing after you've been laying off for a while.
1. Go thrash your way up a 5.14a crack, spray about how you're almost there, down grade it, and claim you just couldn't do it because you're "off the couch"
2. Approach climbing with some humility. Chances are you remember you're best, high performance days of climbing last season, and not the average days. Take the time to build a solid base of fitness. Climbing technique doesn't leave, just the strength. The more you climb a certain grade, the more you will be able to pick up at the grade if you take time off.
The second option is definitely the better one. The most important thing is to get out there and do it. Getting to the gym, to the crag, or out to the boulders can be difficult, especially when you're not climbing your best but the best way to climb well off the couch is to start climbing. Now head out to the nearest Touchstone gym and start cranking