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 strengthen your relationship with a player if you sign the backroom staff member they have highly recommended to you.