Trim, trim, trim
Should be taught in the PPL but often isn't.
But to be fair, it is hard to hold altitude if flying in turbulence. It's hard work, and vertical excursions are accepted - so long as you are not flying 100ft below the base of CAS
In VFR, OCAS, altitude is not important legally, but one should aim to fly accurately in general. Then, when progressing to instrument flight, it becomes a lot easier.