Taking in factors like position scarcity and best overall value are fine, but there are some differences between drafting in an 8-team league verses a 12-team league.

Speed - The obvious difference is the speed at which you picks come back to you.  If you are not paying attention you may lose your place and get caught off guard.  In an 8-team draft, pick your next target position, or identify your next 3 players that you want.

Position Scarcity - This theory plays out more in a 12-team league.  Even in a 36 round 8-team draft you will be picking studs and solid fantasy players well into the 10th round.

Pick of the Litter - Pitching is the one position that will allow you to take great value late in the draft.  This is especially true for middle relievers.  All of the closers are taken, but all of the great middle relief pitching was still on the board.

My best advise for drafting in an 8-team league is to take what is best available in that round.  Don’t try for those long shot sleeper picks until later rounds.  Also, do not be afraid to take great setup men like Shields, Soriano, Duchscherer, and Zumaya.  These players will have a greater impact on your team, especially in roto play, then chasing shaky closers in the late rounds.