you probably haven't got a pipe thermometer, but the flow of water is meant to be slowed enough to give a 20 degree C temperature drop through each rad (otherwise all the hot water will rush through the easiest ones leaving the others cold) but a good rough guide is the flow (input) pipe should be "too hot to hold" and the return (output) pipe should be "too hot to hold for long"
Turn off the heating for an hour so all the rads are cold before you start.
Almost all the adjustment in a lockshield is in its first turn from shut, so screw them all down tight, then open the first one just half a turn and turn on the heating. Wait five minutes and see if it has warmed up. If so, leave it, and do the next. Don't adjust it by more than a quarter of a turn at a time.
If you haven't got time to do them all, turn down the hottest rads, and this will force water to flow through the coolest ones. But as I say, you have to turn the lockshield until it's almost closed to make any adjustment.
The rad in the room with the wall thermostat should be adjusted to heat up slowest.
If one of the rooms is relatively large, with a relatively small radiator, you can let it get a bit hotter than a large rasdiator in a small room.
If any of the valves starts to weep water round the spindle while you are working, screw it quickly either all the way shut, or all the way open, to stop the leak, and see about getting it replaced.
Have you got thermostatic radiator valves? If not, you will have to make further tiny adjustments as Bureni describes, to avoid underheating/overheating individual rooms.