I don't have the experience that alot of posters have, but I also value the health stamina stats when looking at comparing guys, a guy who looks slightly better but have lower health and a lower stamina may not be on the field as much as a guy with a few points less in some catagories but can give you a sure 130 plus games.
I tend to avoid anyone on the ML roster who doesn't have at least a 75 health. Try to remember (and more experienced users correct me if I'm wrong) each play is looked at individually, when the play starts (the pitch) the program looks at it has an individual event. Each player is checked for injury, is the result a hit or an out, if a hit, are there men on base if so, what are the fielding stats of the player who fields the ball, the running stats of the men on, and the settings of the manager, if an out, was it a strike out, fly out, ground out, are there men on base etc. If you think of it lke a decision tree in your head, it helps you look at the ratings and decide who is better and who is more of a AAAA / AAA guy only.
Also beware of small sample size my team in 7mickey7 Jakcsonville, had several players who hit well below what the ratings indicated the should. Over the course of the season, they adjusted to the mean and hit about what I think they should have. Don't be to quick to pull the trigger on a trade if a guy isn't hitting 30 games in.
And most of all, definately hook up with a mentor tecwrg gave you the best advice you'll ever get.
Good luck, hope you have fun.