..from recent experience, a coupla tips.....
...on the engine idle check, ensure it idles at a proper low rpm, got caught out with a Grob the other day which idled at 1000 RPM and wouldnt settle down at roundout.
.... on pre-takeoff checks on Fuel..... ensure Primer locked. No, it didnt happen in the air, it happened because i taxyed to the pumps before preflighting it, and the previous person had left it unlocked..... wonder if he/she knew why the engine was running rough?