I do a lot of Fantasy Football and here are a few comments and suggestions.
If possible pick players who will play every week (or most weeks). So for example Darren Bent will play every week for Aston Villa, whereas Berbatov wont play every week for Man U.
Most of the top clubs have large squads and rotate a lot, so it is sometimes best to pick some players from smaller clubs who have more "regulars" (Everton, Stoke or Sunderland for example).
Go for defenders from teams who let in few goals (obviously). Last year this was (with best first): Chelsea, Man C, Man U, Arsenal, Fulham, Liverpool, Everton, Spurs, Stoke (though Chelsea and Fulham have new managers).
Pick defenders who score goals or take free kicks or penalties, or attack a lot - Huth at Stoke, Baines at Everton, Hangeland at Fulham, Johnson at Liverpool for example.
Pick midfielders who "attack" and score or make goals - Van Der Vaart at Spurs, Malouda at Chelsea, Nani at Man Utd and so on.
Pick strikers who play regularly (obviosuly), score goals (obviously) and if possible take penalties - Darren Bent at Villa, Van Persie at Arsenal, Rooney at Man Utd for example.
Think about teams in Europe, particulalry those who have to start their campaign early. For example Arsenal have to start in Europe right at the start of the season, whereas Man U and Chelsea start later. Ths may cause more squad rotation (and injuries) for Arsenal early on.
Note that Liverpool are NOT in Europe so can focus more on the Premier League (not sure if Sky Fantasy includes Europe matches).
Avoid players who get booked or sent off a lot, or are injury prone.
It is the African Cup of Nations in January 2012 so lots of African players will go off for a month or so (Drogba at Chelsea amongst loads of others).
A fantasy team is a compromise between cost, players, teams etc and can take quite a while to get "right".
However the best planning in the world comes to nothing if your star player breaks his leg in the fist match (which has happened to me in the past).
Good luck.