Try to think about relationships between things. To retain genchem try to link chapters you learned earlier to those you learn later.
For instance look at the links between gas laws to Le Chatlier's principle or the links between thermodynamics to phase changes, etc.
If you can draw the links and relationships, you will be able to retain it better.
Also try to think about what happens if you have a relationship like
PV = nRT. What happens to V as you increase P and vice versa. Try to think of those kind of inverse proportionality vs. proporitionality type or relationships.
Or what about if P increases what happens to n?
My point is look at things from a conceptual view and try to draw relationships amonst different chapters, because you'll retain it if you try to think about it conceptually and try to draw the links. However, if you try to just memorize it, then you'll forget it.
Also, if you try to find a way to apply it, then you'll do better as well.