I don't think there's any way to increase interest per se; I haven't concluded whether season performance plays that much of a role in the interest other teams have in your player.
You should monitor other team's interest; take into account their record and their weaknesses. A struggling team without a good power forward is likely going to be interested in acquiring a good power forward; this may work to your advantage. As the season progresses and a team's need for a certain player or certain type of player grows, so too does their interest in other team's players.