From a basic stats perspective, the leadoff hitter is guaranteed more AB's than any other player. As you go deeper in the lineup you are guaranteed less at-bats. For this reason teams are going to cluster their best players in the 1-4 slots, with their 1-2 batters more often trying to just get on base, and the big hitters in the 3-4 spots focused on bringing them home. You'll want to keep an eye out for players that have moved up in rotation from 5-6 and into 1-4, since their DFS salaries might not have caught up yet and there's some value you can potentially pick up.