There are many factors that influence the final yield of cheese. Yield is influenced by the milk brand, seasonal variation of the milk, the milk acidity, curd temperature, setting time, skim milk powder addition, calcium chloride addition and how the curds have been handled (amongst other factors).
Ways to maximise your yield:
Add calcium chloride (except mozzarella).
Add skim milk powder to your milk (except mozzarella).
Ensure curd setting time is followed.
Use the freshest, best quality, full-fat, unhomogenised milk possible.
Always handle curds with extreme care.