Although this depends on play style, I have found that any formation with RW/LW or RF/LF will increase your chances of getting the top players (Ronaldo, Messi, Neymar, Bale etc). With a little luck you may be able to build a squad with all 4 players available (remember there is a chance one of your subs/reserves may give you the option of picking such a player).
Defensive formations (such as a lone striker) tend to reduce your chances online. Ideally you want something attack-minded. when defending this gives you an opportunity to counter attack in numbers (as opposed to a lone striker trying to cover half the pitch on their own).
I find that the best approach is to aim for 100 chemistry. To achieve this start off by trying to fill the starting 11 with players from the same league. This won't be entirely possible due to the random subset of players available for each position. However, when selecting your subs/reserves you will have a second opportunity to fill in the gaps.
When you are given a choice that doesn't fit your goal of 100 chemistry (e.g. no player from your chosen league is available, or the sub/reserve player options are for a position you have covered) always choose a top rated player (attacking preferably, without worrying if their position fits your formation).
Move your players around so that you end up with a high chemistry team (hopefully 100) and your subs bench filled with attacking talent. This may mean you have a starting line up with Ronaldo on the bench, but this is no problem. You can sub him in any time you want during a game with no penalty to your chemistry. Chemistry appears to lock in based on your starting line up.
A team with low chemistry will make more mistakes in passing, first touch and shooting. Aiming for a high chemistry will give you a cutting edge.
Your draft team are not subject to contracts so all are free to play in each game in the tournament (obviously, until you either win overall or get knocked out). Also, your players fitness will restore to the maximum after each game (so no need to rotate your players through the tournament).
Bringing on 2 or 3 world stars part way through the game can unsettle your opponent, and help in tipping the balance of a game in your favour.