1) Dont be afraid of hard credit pulls. That said, dont accumulate 500 pulls. But having between 2-6 pulls, per year, is not something to fear.
2) I definitely recommend getting 1 card from each of the 4 majors, ie, 1 Visa, 1 MC, 1 AMEX, 1 Discover (yes, yes, even Discover).
3) Consider joining a credit union
4) Assuming you are not about to purchase a home or car, the more cards you accumulate now, the better. So by the time you're ready for a big ticket purchase, you can show a lengthy credit history on numerous lines. I'd suggest visiting one my favorite websites ever,
http://www.freefrequentflyermiles.com and check out a huge list of other annual fee free cards to choose from
5) DONT carry a balance. Ever. Period.