GK start with a keeper, that you are less likely to change through out the season.
DEF I tend to pick one good one, and leave the rest at the end.
MID Again one good one, then average, this is the area where you should look for cheapest players/bargins, since you will not lose points so there is nothing to lose compare to DEF.
ST The most important for picking up points most of the time, pick two of the best ST/top scorer of last season, one maybe less good depending on your defense.
Tip: You do not have to spend all you money, leave some available as this will allow you to make substitutes easier. Give this a read http://www.bbc.com/sport/0/football/33713208
