In order to win your fantasy league, you need the players you acquire to out-earn their draft slots or auction prices, i.e., you must make a sizable collective net profit on your roster. Assuming you're not playing with complete novices, there are four ways to do this:
1. Be a "Genius"
The Genius draft style presupposes you're able to predict which players will over- and under-perform their median expectations as set by the market. Essentially, it's beating the market by being wiser than the crowd. The market has Jason Heyward as a sixth-round mixed-league pick or at a $22 NL-only auction price? You believe he's worth a third-rounder or $28, and so you draft him late in Round 5 or buy him for $23. If you're correct, he's part of your roster's net profit.
2. Be "Agnostic"
The Agnostic draft style presupposes that no one can consistently beat the market over time, and that the wisdom of crowds is too great for an individual to overcome. The agnostic's strategy then is to let the "geniuses" draft for him. If Heyward is being taken a round early or for $2 too much, then someone else - usually some steady, unsexy veteran like Lance Berkman - is necessarily too cheap. There's a set amount of money to be spent on the eligible player pool, so if the prospects and upside players are going for more than their market values in your particular auction, the steady veterans must be discounted. The agnostic simply picks up these discounts along the way without preference, much like a Vegas bookmaker will let the bettor choose the side, and happily collect his profit from the vig.
3. Get Lucky
I don't know who drafted/picked up Jose Bautista in my leagues in 2010, but I assure you whoever it was (a) made a massive profit; and (b) had no idea what he was getting at the time. Sometimes you make a huge profit simply due to dumb luck. It can happen to anyone, and it's not something you can count on or reliably repeat.
4. Gamble on Hard-to-Price Players
Many players are somewhat hard to price. I mentioned Heyward - one of the top prospects in the last few years - who had a bad second season due to injuries. He's apparently healthy now, but it's unclear whether he'll pick up where he left off his rookie year. I also mentioned Berkman, a 36-year old who looked finished until last year. Is he back for good, or was last year his last hurrah? But difficult as those two players are, we have most of the key information about them, and the market prices for them are likely to be somewhat reasonable and efficient, as most people know what to make of them.
But there are other players - Chase Utley (degenerative knees, starting the season on the DL), Justin Morneau (ongoing concussion), Carl Crawford (DL with a wrist injury), e.g. - who are even harder to value. And I'd argue that the market for them is not efficient because the information on them isn't good. Even the medical establishment has no idea if or when Morneau's concussion symptoms might recur, and Utley's knees might or might not respond to rehab. As a result, many people simply steer clear of these players altogether, preferring not to draft them and reasoning that they'll let someone else "take the risk."
But risk and return are inseparable, and the more everyone else is blinded by fear of what could go wrong, the more potential for profit there is. This isn't a "genius" strategy of taking a player you like - you might have no special insight into Utley's or Morneau's situation. But you're simply gambling that fear is artificially depressing their prices relative to their expected returns and positioning yourself to profit accordingly.
In the end, how you get there doesn't matter. The key to winning your league is to accumulate more net profit than the rest of your league-mates and figure out how to distribute it appropriately across the necessary categories. You will need some luck, you might have a better read than the market on a couple players, you'll probably have to grab a couple players simply because they fell to you at a great price, and you might even want to gamble on hard-to-value players that no one else has the stomach to own.