30 or so lbs should be best for your normally HVLP guns. Check your instructions. YOu have to play with the gun and thin out the material so it go through the gun a little easier. sometimes you have to go over the same spot or tube twice for an even coverage. If it orange peels, you are putting out too much material. Back it off and let in a little less air. YOu should be able to do that with a knob at the gun. I normally keep my air pressure around 35-40 lbs and play with the inlet know. I have a bleeder valve at the hose to relieve pressure. We use to spray lots of lacquer, not so much paint.

Try and shoot something flat like a piece of MDF with primer already sanded. This way you can see your spray pattern and adj your gun accordingly. For someone with little experience with spraying, it is too difficult to see the result on a round tube and make corrections and adjustment right the way to dial in the gun for a specific material.