Here's my squad as we start the 2nd half of the season...
And some more explanation of the positions...
GK - Keeper. Gets 50% bonus to defense and control when in goal.
SW - Sweeper. Automatically moves in between player with the ball and the goal.
CD - Central Defender. Automatically tries to tackle someone who comes into and adjacent tile.
DF - Universal defender. Tries to intercept shots or passes that come within an adjacent tile.
LD/RD - Fullbacks. Decreases the ability for an opponent to use a special skill. Can move 3 tiles.
LM/RM - Wingers. Can move 4 tiles with the ball and spends no action points on pressing.
MF - Universal Midfielder - Can play anywhere and move 2 tiles with or without the ball.
CF - Central Forward - Automatically moves into any gap near the opponents goal at the beginning of a turn.
D, M, or F - Amateur positions. With more experience, they can learn one of the above positions.
? - Need to learn an amateur position first.
You get experience based on where you play, so if you want someone to become a fullback, you have to play them on the flanks so they get experience there.