This tip is meant to help players that encounter issues with maintaining a relationship with the Mafia that ensures Jack's survival.
If you don't want to carry out Mafia assignments or don't want/can't spare to send policemen to the Mafia calls, than you can improve your relationship by selling to them confiscated weapons, drugs, jewelry and any item your cops may find after completing a call.
This can be useful at any point of the game where Mafia assignments are scarce, and especially after a certain point in the game, where your relationship with them does actually degrade over the course of days, no matter the decisions you make.

Cheers.