CPU teams are really for free players to try the game and for troll builds. Once you are ready to spend money you will move into player teams and more importantly coaching and leave the CPU games behind.
The real competition happens on player teams. A general rule of thumb is to never accept an auto-offered contract. You get these when you "request contracts". You will only get offers from CPU teams (bad) and inactive player teams (worse).
During the offseason I would try to post in the recruitment forums and create a marketplace add for your player. Finding a team on the middle of the season is difficult unless you ask an owner what he wants and then create a new player just for him. This is because most rosters are set when the season begins and anyone who changes teams (from a CPU team to a player team) arrives with zero chemistry and will play at a reduced level.
It's good to know that you can retire your free player (if you are on a CPU team) and create a new free player. It is also good to know that you can lower attributes below 5 to increase other attributes.
Good luck!