New tattooist

Hell all my name is Mike im 34 and have just started out tattooing about 8 months ago i have tried practice skins, grape fruits, bananas, and pig skin.. i have been doing tats on a few friends who are to cheap to go have them done by a professional..i do have a few questions on tuning i have got about 8 machines but only 3 work consitantly. but my real question is in shading and getting the different types of blacks. any advice would really be helpful.