If you have, let's say two shortstops on your roster and you keep switching them in & out, you'll hit 162 games played before the end of the season.
Some little things are:
In Yahoo, they have a screen where you can see what a guy has done over the past week, month and season. Check these, because guys run hot & cold. You'll get a feel for how that player is playing, and what stats he is producing. You can balance your lineup that way.
Try to always start your 'Aces'. These guys are aces for a reason. Pitchers you consider "fifth starters" in your league can be rotated off your roster. The "fifth starter" on a fantasy team is usually a guy who is on a roll, getting huge stats in a needed category or facing a bunch of crappy teams.
Don't panic early on. If a guy has posted consistent stats for a few years, hell probably do it again. Guys off to hot starts happen every year, and they usually fade back to where they were. Don't trade Aubrey Huff for Tony Womack.
Don't make trades just to make trades. Go back a few seasons with a guy's stats and see what he did last year and the year before. Some guys, like Chipper Jones are consistently good players, the same goes for the bad ones. Make trades if it makes sense for your team.
Also, if a guy offers you a stupid trade, offer him a counter-offer. I've found that you can usually take advantage of idiots like this if you are nice to them....lol. Don't just offer him a dumb trade in return. You'll catch more flies with honey than vinegar.
Have fun. It ain't a job, so treat it like a game. It makes learning about all of baseball more fun.
-The Self-Proclaimed Voice Of Truth And Reason-
-Your Friendly Neighborhood Slapweasel-
...I'm Your Huckleberry.