Learned this the hard way. You are supposed to pack the oil pump with grease or assembly lube, so that it will create a vacuum and pull the oil up the pickup tube on startup. I did not know this, and could not get my oil pump to prime. Pulled the spark plugs out, spun it over, no oil pressure. Here what you do if you have done this.
Pull spark plugs out of engine.
Take out efi relay in fuse block.
Take out dipstick.
Use a air nozzle with a rubber tip, stick this to the end of the dipstick tube.
Have a friend spin the motor over while you blow air into the dipstick tube.
The positive pressure will push the oil up to the oil pump after a few turns.
Don't spin the starter more than ten seconds, and wait a little bit for it to cool before you spin it again.

 

I didn't have a problem getting pressure when I did mine.. Just put it on there and fired it up, made pressure quickly..

I have heard you can take out the pressure relief bolt and spring stuff and put oil in there and it will help prime it too

 

Unusual as gear pumps are positive displacement pumps and are self priming in automotive applications where they don't have to lift much. NPSHr<NPSHa

 

I tried the pressure relief bolt first. Filled it with Lucas. Spun and spun but never picked up. Figured I'd try this before I took the oil pump back off to pack it.