Success at fantasy baseball is all about adjusting to context. Sometimes the context comes within the game of baseball itself - for example, adjusting for park or for league strength. Other times, the context is found within the rules of the fantasy game you're playing.
One such example is making adjustments for the size of the daily contest you're playing. Sites like FantasySportsLive and DraftHero run contests with as few people as two to as many as fifty. Your strategy needs to change to reflect the size of the contest! Two person contests are the most straightforward - you're generally going to do best simply picking the players who you believe will score the most points that day. But isn't that true in larger contests too? The answer is...definitely not! If you use the same strategy in a fifty person contest, you're going to frequently find yourself finishing in the upper half of the contest...but falling short of the top few spots that receive all the prize money.
The goal in a larger contest is to introduce variance to your scoring. Note that this strategy won't work (at least as described here) in a season long contest like Rotohog, because those have a real 'penalty' for putting up especially low scores. But in a single day contest you should be looking for strategies that will increase your chances of having the top score...even if those same strategies will also increase your chance of having a truly awful score.
There are really two things you can do to accomplish this:
1. Choose players whose performance is likely to be strongly correlated. The easiest way to do this is to choose players on the same team. If they knock the opposing starter out early and get to face the dregs of the opposing bullpen, that's going to benefit both of them...leading to a positive correlation in their scores for the day. If the batter hitting fourth gets an RBI, there's a pretty good chance that the batter hitting ahead of him got a run...again leading to greater correlation among their daily scores. Most games won't allow you to choose all players from the same team, but choosing mostly players from the same team is definitely a good idea in larger contests...particularly if you can identify a bad opposing starting pitcher to go against.
2. Differentiate from your opponents. This is a little trickier. In order for it to be a viable strategy, you need a few conditions to exist. Score should be heavily influenced by one player...for example a game format where a single starting pitcher generally scores almost half of a team's points for the day. You need to know that most of your opponents are likely to choose the same player for that position. Imagine a game with 20 contestants where the ENTIRE score is derived from a single starting pitcher. Now imagine that there are only two starting pitchers available today...Jake Peavy and Mike Pelfrey. Who is the better pick? Almost certainly Pelfrey! While Peavy might have a 75% chance of winning, if you win you'll be sharing your first place prize with about 18 other people. If Pelfrey wins (25% chance) you're likely to win the entire prize. This is a great (although admittedly extreme) example of how differentiation can help you in these contests.