I'm fairly new as well but am learning quickly.

I am personally staying away from credit cards because I am young, have student loans, and don't want to bother messing anything up accidentally (even though many people say I won't).

I am currently a member of AAdvantage as my primary mile
account and Delta and United as secondary accounts. I'm learning that you can earn a good chunk of miles at a time (1000-5000) by doing promo deals. I know they aren't large sums but slowly but surely, you'll end up with some solid mileage.

I signed up on TravelHacking.org ($1 for a 14 day trial, $15/month after that) to have automatic deal/promotion updates. He walks you through a lot of the details of "travel hacking"/flying with miles step-by-step. And you can always cancel your account if you feel like you've learned enough in 14 days. But keep in mind he actually offers a guarantee: earn 25,000 miles in 3 months (100,000 a year) or he'll compensate you. He also doesn't push you into credit cards. He agrees that they are a good way to get tons of miles fast but realizes that those deals aren't for everyone.

Happy Travels!