1. Remove the pump and ensure that it's clean.
2. Make sure the rubber bubble adjusting hose isn't being kinked
3. Those skimmers are very sensitive to it's sitting water level. If the skimmer is above or below the water line you may get less than optimal results. Also, be sure to keep up with your water top-offs. As mentioned before the skimmer is very particular to water levels.
4. Ensure the water intakes at the bottom of the skimmer body are clean and clear flowing.
How much skimate is extracted correlates to the bioload in the tank. If you have a low bioload you won't have much skimate.
Chris
Good luck.
Good luck.