what i usually do is go look at who my 2 start pitchers are that week. 2 start guys can be very valuable, especially if you need help with K's. theres usually plenty of sites that come up on a google search for "week *whatever* 2 start pitchers". i usually go with all the 2 start guys, unless i really dont trust them, or i have too many 1 start guys who are clearly better.
you also obviously want to look at the pitchers recent outings. if theyve been sucking, for example Chris Young (which is a direct relation to his back problem), you may want to sit them down. unfortunately, my rotation, which includes Young, Bonderman, King Felix, Javier Vazquez, James Shields, Ben Sheets, Rich Hill, and Roger Clemens, is riddled with great pitchers who are recently struggling. i decided to sit Young, Vazquez, and Clemens (for good reason.) so far the strategy of going with the hottest hands is working. Felix looked good, while Chris Young was terrible.
You also want to check out who theyre facing, but IMO that isnt as big of a factor as people make it out to be. if youre on the fence, go see how theyve done against the team their facing this season. unless theyve gotten smashed, i wouldnt use that as a reason to sit them. you can also go as far as to see how the opposing offense theyll be facing has been hitting lately.
BN Bautista Victorino Utley Machado Stubbs W.Chen Marcum J.Garcia
SP Bumgarner Hellickson Scherzer Ed.Jackson Lynn
RP Papelbon Putz Street