Instructions
Look through your team stats at the "Stats" screen and find out where your team is weak. For example, your team may have a hard time making three pointers or may have a tendency to pull fouls. Pinpoint areas you'd like to improve.
Search through your player stats to find a player that is weak in the area you want to improve. You may need to choose several players that are weaker to find a player that is stronger. Take note of their monetary value as this will be important in trades.
Look through your other team's stats to find a player that you think can improve your team's deficit. This player may be more expensive than your other players, as he will be a better player than normal. You may have to trade more than one player.
Make an offer to the team for the player you want. They may reject your offer or demand more players or more money. Before making a decision, make sure the players you are losing aren't strong in a stat where your new player is weak. For example, if you are trading two strong three point players for a better defensive player, make sure you have enough good three point shooters on your team to make up the deficit of their loss.
Adjust your trade to suit the needs of the other team but don't give them everything they want at first. Haggle with them; offer them a little bit less money or one less player than they want. They will decrease their demands a little. Repeat this process until you get a trade.