I'm not totally saying ignore rookies, but be really selective about it. The fantasy baseball world seems to have a new the "next big stud" every week. If you look though at most veteran studs today, nearly all of them didn't start out as studs. Some were practically nobodies their first few years in the show. But as a general rule, there's a learning curve to becoming a stud in the show, and the last few lessons take place in the show, not while in the minors.
The thing is, it's a question of time. 9 of the 10 "next big thing" either doesn't pan out or they take a year or more to really develop. There's such a HUGE chasm between the minors and the show when it comes to the talent level that I don't place huge importance on a guy in the minors who's raking mediocre pitching or dealing against mediocre hitters. Shutting out a team full of 20 year olds is easy, facing Jeter with 2 guys on base and no outs is hard.
I also don't totally buy into a new call ups that start hot... lots of times, it's due in large part to the fact that the show hasn't figured out his weakness or tendencies yet.
Generally, I'd rather spend what limited research time I have looking for that 2nd or 3rd year player that's taking his game to the next level. Guys like Ortiz, Utley, Alex Rios....
In the last five years, I've jumped on four rookies, Miggy Cagrera, Carl Crawford, King Felix, and just recently Kendry Morales. Cabrera and Crawford have definitely paid off and I expect them to get even better, I think King Felix will eventually be a stud, and since I had a slot open up and he was on the wire, I jumped on Morales. If he doesn't pan out it doesn't cost me anything.
Cabrera, I jumped on when he was hitting in the show at 19. When a 19 year old can hack it in the show and doesn't even choke in a world series, I'll move heaven and earth to grab those guys. Crawford because of (A) his speed and (B) his age. King Felix, like Cabrera, because of his age... Pitching decent late last year at 19 is just mind-blowing. He's having some rough starts, but he's racking up Ks, so I think he's just missing his location occassionally, something that's fixable in time. The potential upside in the years to come is worth nursing him on my pine for now. Morales was cheap and he's raked in his first week, so I took a flyer.
But these are the exceptions, I don't trade a cold veteran stud for next week's Cole Hamel.
Another thing is, I try to tune out the hype of all the so called experts... I do listen to what veteran players and coaches say. I heard Lou Pinella say Crawford would win a few batting titles before he's done. When guys who really know the game (i.e. played it) predict greatness, my ears perk up.