I have a 4yr old dog I rescued and one of his issues is dominance. What are some ways to correct his issue and what to look for?

It really depends on if you are trying to show dominance over him or another dog is. If it's another dog, let them sort it out. If it's you, holding them on the ground is a good option if you think it's safe. If you feel the dog will bite, then obedience classes are the way to go.

Obedience training and lots of exercise.

You do not need to dominate the dog but you need to be able to control the dog.

You don't say what the specific problem is.

To show a dog who's more dominant pin him down on his side (not hard) and state in his eyes to show him your the boss

I agree with "tigrillen." Dominance theories are out-of-date and have been proven inaccurate. Lots of exercise and training will help correct his issues.