I use a medium to heavy filter especially on primer, primer seems to often have alot of junk in it and plugs up those filters fast might want to screen the paint first .
In the gun I use medium filter for latex and 5/15 flip tip, alot of guys like something finer like 4/13-15 theres less bounce back spray if you keep the pressure down a bit. If you do anything where you need a nice fine mist I use 4/11 like cabinets and doors, baseboard and door jambs if there done separately.
ALWAYS remember when spraying to stay back at least 10-12 inchs otherwise you end up getting lines and holidays , further back the better it seems. I often shoot a wall at around 12" then sweep back and cover it again a bit further back to lay down another light coat on top of the heavy one it covers anything you might have missed.
Don't forget the rig cleaner
thats essential to keeping the lines and pump clean