I was told: Open the wheel valve/thrmostatic valve fully, screwdown the lockshield and re-open it until, with your ear against the radiator, until you can just hear the water running through it. Stick a couple of magnetic thermometers on the radiator, few quid from Amazon, one on the inlet the other on the outlet. Gradually open the lockshield valve until you get an 11 deg C temperature difference across the radiator.
Start nearest the boiler/pump and work away from that point.
If your radiators have been sized correctly you should find that the radiator temperature will be adequate for the room. If you find the room is overheated keep closing the lockshield until you're satisfied with the temperature.
It's a lot of messing about, probably why it doesn't get done very often. You'll need to go around quite a few times over a period before it settles.
Although it sacrilege to say so, I've never advocted thermostatic rad' valves (personal opinon, you understand, probably in a majority of 1) unless you have a room with a high external thermal gain as they often get stuck closed during the summer and freeing them up only makes a job for the start of the heating season.