The midfielder: at the heart of the game
Of everyone on the pitch, the player who has to work hardest on positioning is probably the midfielder. The thinkers of their team, time is valuable for them. The more of it they have, the more easily they'll be able to move their team in the right direction. Sergio Busquets, for example, has a talent for always getting himself and his team-mates into a comfortable position. To do this, he's constantly analysing the movements of his partners and opponents. He keeps his head up so that he can more easily spot gaps or move himself into them to get free. You don't need to run miles to do that. Just standing a few metres back will do the job and gain you a precious few tenths of a second.
For midfielders, adapting to their team-mates is also vital. If you're playing with two or three in midfield, watch what the player(s) either side of you is(are) doing. If another midfielder has moved forward to attack, it's up to you to be smart enough to hang back so you can kill off any counterattacks. This won't stop you having your moment when the opportunity presents itself. And this is where another key aspect of good positioning comes into play: communication. Keep talking to your nearest team-mates so you can adjust your position and make it as effective as possible.