My experience is "cavitation" (air in pump) is a bad problem.

I do these:

1) use a larger inlet pipe (larger than a outlet pipe) and put the pump not too high from suction point.

2) run the pump at 'right' speed (run too fast - make air bubbles; run too slow - not much water pumped to target)

3) clean the propeller/impeller - rough surface makes more air bubbles; smooth surface = less friction/power too.

Modern day pumps come with one-way valve, so we don't have to prime ('fill the pump with water) first anymore ;-)