One of the biggest mistakes that players make is to focus on how much money they will win from a bet, as opposed to how likely that bet is to win. It means that they often wager large sums of money on short odds or place bets on high odds just for the sake of it.
Neither of these things are advisable, so the best thing that you can do is just focus on the most likely outcomes (based on your hunches or research), place your bets accordingly, and then see how things go.