A good way to help avoid upsetting a dropped player is to warn him that you plan to rest him in advance. The player is less likely to get upset if you tell him you intend to rest him prior to the game.
A player is more likely to agree to a rest if he is starting to feel jaded, especially after a tough prolonged period of games.
When resting a player, choose the length of rest carefully as many players don't enjoy being out of action for too long.
Once a player enters the latter stages of his playing career he will start telling you his long-term plans. This will give you an idea of what he wants to do when he hangs up his boots.
A good way to strengthen your relationship with a player is to sign someone they have recommended to you.
You can have more control over the way your players play by asking your coaches to 'Start Preferred Move Training'. [New in FM12]