When you say one pec is noticeably larger than the other, do you mean there's symmetry between the two, just a major size difference; or structurally you lack the symmetry? There's really only so much you can do if the issue is the latter; even isolation work can't fully account for fixing that problem, but it is the best course of action.
Something that always helped me is to work the chest with a wide range of movements; incline, flat, decline, etc. and not just focusing on one particular movement (most tend to hyperfixate on incline pressing movements)