What are the tricks to lower down an AC contribution in electricity bill?

Take cold baths, use the microwave rather than the oven or the stove, and draw the drapes in rooms that get a lot of sunlight. Also, don't put on the AC unless you really need it and keep it at a temperature that is better than the outside but you don't need to be freezing.

Check for air leaks around doors and windows. Check duct work for leaks.