How to get this finish?

[magicniner]

For wood that has to look super-smooth you need a sealer coat to stop the thinner from subsequent coats deferentially soaking into the wood and creating "sink marks" which reveal the substrate texture.
Follow that with a self-levelling primer, then your finish coat. If the primer isn't 2-pack you may still get a slight matting/texture to the finish surface as thinner will leech out of the top coat into solvent evaporation drying primer giving a less than perfectly flat finish.

You also need a clean environment to spray in, ceiling and walls should be cleaned with clean wet cloth and the floor is best mopped and left wet to prevent any dust.
If you build a polythene sheet spray booth inside another structure a clean air flow with positive pressure is ideal, as is air-fed breathing apparatus.
For small items it's possible to build a spray booth like a blast cabinet with painter and the process air flow kept completely separate,

- Nick