If you are seeking for some Football Manager 2012 tips and hints then I advise you to read FM2012 hints and tips post.
Usually playing Football Manager 2008 I follow the next principles when it is necessary to select the first squad before a match:
• At first when you select players for participate in the match, look at their morale and conditions. Try to use players with the highest morale, and do not set to the first squad 'Very poor' or 'Poor' moraled footballers.
• As far as conditions concerned, usually I do not use players who has less then 94% giving them rest from the game or just placing them to the substitution.
• Another small hint is checking current level of fitness of a player. I never set a player to the first squad when he has fitness - 'Several lacking in match fitness', 'Tired' or something like that except matches with very weak opponent teams.
• Never set injured players with orange 'Inj' sign to participate in a match.
• It is also important to understand form of your footballer: how good he played last matches, what kind of performance he shows during this season, how often he gets injured, how good he is at that or other position where you use him. Follow statistics of a player!
• Talking with players during the matches, correct media comments and personal talks with a player really matter!Use them often to increase morale of your footballers. Try to avoid setting to the first squad a player who is being nervous before a match after your media comment.
Other information concerning tips and hints:
Some thoughts about player conditions, training workload and rotation
5 Helpful Hints for Football Managers