I am going to buy my first fallout game soon and I have a few questions

Fallout 3 or Fallout new vegas?

Xbox 360 or PS3 (I would prefer PS3 but beth games have a history of being better on 360)?

Any beginners traps I should be aware of?

that's kinda it, thank you for anwsering

Both but play fo3 first.

I'll go for Fallout 3 first, it has a greater atmosphere, and I believe this is the most important thing for a first impression. New Vegas has its better things, but like John Henry, I think they are better to be play after Fallout 3.

Hope it helps!

EDIT:

As for the platform, if you can, PC. There are sooo many mods you can enjoy. Although I havent play them because I play on the Xbox 360 and I cannot advice you about which console is better since I never try it on a Play Station 3.