Week to week it's a crapshoot. To stop this from getting AC-ed, I'll keep it general.
On draft day, I look for three things in a kicker:
1) A good offense. Teams that lead, or think they will are more likely to "settle" for field goals, either early in the game, or when they are up big.
2) Plays in a dome or warm weather. Two reason: good kicking conditions year around - but especially in FF post season (when weather is bad).
3) Strong leg. In my main league, we get bonuses for long field goals - so I guy like Seabass is worth quite a bit as he is routinely put out there to nail 50+ yarders (unless his QB takes a sack on 3rd down to take him out of range!)
To a lesser extent, same thing on a weekly basis. Which of my kicker's teams is going to be winning? Will weather be a factor? Who's better from distance?
But honestly, if predicting actual NFL games is difficult, how much harder is it to think "This offense is good, but will bog down at about the 30 a few times for good kicking opps." - close to impossible. Just be better everywhere else in your lineup, so it doesn't come down to kicker [/screech!]