I rate, preseason, and constantly update, all starters 1-5. Clemens, Santana, they're 1s. Nomo, Darren Oliver are 5s. (I basically use rotation orders, with some exceptions when a 2 is a 1 or a 4 performs like a 5.)
Then I track each team's W/L vs. 1-5. At least until June, it helps me see who has been beating up on lower-rotation pitchers and who has been abused by ace after ace.
(I will also watch righty-lefty records and lineups, as was previously mentioned. Some young hitters with high averages will get them by sitting out against LHP. Check Hank Blalock's career vs. Lefties, for instance.)
By July, pitchers with holes in their arms will begin to reveal themselves. Erwin's pitching aces is as useful in midseason as in April. More, I think. Can help predict streaks (a scary proposition, not for the weak of will, but glorious when you're ahead of the curve).
In August, I go with Madcapper. Don't know what he does, but it's good.
In September, I find pitchers who aren't weak, who will persevere, and bet their hind legs off. Nothing like a team on a September roll, because so many are passionless by then.
I believe strongly in lineups, and will avoid overnight lines on getaway days, or any day I have reason to believe critical offensive players are sitting.
Other factors weighed: 1/ Rematches from previous week are common in the era of the unbalanced schedule. I don't like a guy to beat the same guy again next week. Either flip or pass.
2/ Your ace is playing their No. 5 on the road and I'm guaranteed nine at-bats, I just might play the run line.
3/ With daylight savings time, you have an early evening start for ESPN -- say 5-6 local time, I will play the under even with poor pitchers on the mound. That twilight dotting the field with shadows screws up hitters bigtime.
4/ Managers tend to follow one of two philosophies about lineups. Most believe in a healthy mix of Rs and Ls in the batting order. Some stack their lineups, grouping Rs at one end of the order and Ls at the other. That is a mistake, especially against a weak starter who might not be on the mound long. It invites a manager to lineup his bullpen, using specialists for not just one batter in the sixth inning, but the entire inning. Another for the seventh, then he has his setup man and closer. If you can't get to them, you've robbed yourself of at least four innings to beat a bad starter. Bottom line: Bet against stacked lineups.