Here are some what I think are helpful tips:
1. LEGO can be expensive
That's why I buy for less whenever I can. There are many ways of acquring LEGO and if you are building specific sets there are loads of instructions on the web (go visit brickset.com) and getting parts for them (bricklink).
2. LEGO can be tiring
Sometimes after two hours of staring at the little booklet trying to finish building the set, you get tired hunched in your seat, your eyes hurt looking for pieces and trying to figure out how to put it together, etc... So sometimes it is nice to have a small side project like building minis or looking at other things.
3. LEGO is hard to sort
If you are building models only then you won't need to go through tens of thousands of little plastic bits but if you are go look for a plastic tool box with lots of drawers to store different pieces and small tackle boxes for smaller pieces, also having a gigantic box is nice to keep unsorted or 'scrap' LEGO
4. Have Fun
The most important part is to have fun for that is the whole purpose of LEGO, it even means that in dutch (I think) play well.