welcome to ft!!
it depends on what you have time for also... this is a hobby and an addiction for many of us (for me it's a sickness

) and so you need to be able to devote to it what you think you can manage. It's not always glamorous and easy to earn miles and then redeem them like you see on TV. You need to become as savvy as possible to what is doable within your own world and mindset.
As said earlier, do figure out roughly what some of your travel goals are and of course, destinations with relation to where you live and what airlines best serve your needs. For example, in Boston, MA, USA, I find the best way for my wife and I to get to Amsterdam is with NorthWest because they fly direct.
For flying to Maui, we would go with AA because they are easiest to redeem on.
For hotels, we like Starwood.
I like United for some ski trips and travel to places like Chicago and California...
I therefore have a membership on each of those programs and also, it is noted that with the airlines, at least, there are "alliances" that help serve you when flying on other carriers!
Learn about the credit cards that give you points/miles, and get to know what these partnerships of airlines are (found on airline web sites and also in here) and pick one of each, should that match your needs.
I would also always stress this point:
Whenever you deal with ANY mile promotion or offer of ANY kind, SAVE all paperwork, receipts, tickets, voucher copies, and whatever else goes with it until AFTER you see your miles post. There's nothing worse than to be promised something only to see nothing and then have to go prove it later on un armed.
Good luck and welcome to FT!

MM