It may be your technique more than your paint.
Try thinning the paint just a bit more so that if flows smoothly after
its on the surface.
Be sure you put enough paint on the surface so that it can flow.
After you have put the paint on, lightly brush the surface at 90
degrees to the direction you applied the paint. Called "tipping off"
The only way to get a purely flat surface is with a spray gun,
electrostatic spray, and lots of other equipment.
BTW, I've gotten fairly good results with spray paint out of a can, if
you can find the color you like. The good (not the cheapo) paints seem
to go on smoothly, and flatten out as they dry. Practice spraying
first, there is an art to it.