well it's a good thing to know how to make small adjustments to the truss rod. The key thing is to do it a little at a time, and if it starts feeling like you're fighting with it, or like it's getting too easy then you want to go back a bit and consult an expert. I'd recommend turning it about 1/8 of a turn at a time at first.
Remember that we're going into winter now, so the air is drying out, and if your guitar is all solid wood (IE no laminates) or even just has a solid wood top then that will start shrinking and that will have an effect on action too. Typically in the winter the action should get lower and if the guitar was well set up it may start buzzing when that happens.
NOW.... all that said, the truss rod is not meant to be used for adjusting action. It's meant to be used for adjusting neck relief - which will effect the action, but is only one factor effecting the action. So it's not a cure all for action problems.
If your guitar was set up for 11s, the neck may well start bowing a little with 12s on. Again this is not the only aspect to achieving a good setup with the heavier strings, but it is something that needs to be looked at.
Now check out
http://www.frets.com/FRETSPages/Musician/GenSetup/TrussRods/TrussRodAdj/tradj.html
It does no harm to understand what a truss rod is, how it works and what it does. The author does get onto the adjustment eventually. Note that this is done with the neck under tension and at concert pitch. You can use a capo at the first fret in place of one hand - I find it's a sort of three-handed job myself.
But go
GRADUALLY at first. You should be tightening it a little to compensate for the extra tension in the 12s. Baby steps!
1/8 of a turn at a time, and if things get weird or worse than go 1/8 back the other way and take the thing to a good technician.
REMEMBER: If it starts getting tight or starts getting loose then you're about to over do things and, again, you want to consult a good technician.
