At its simplest, even in lousy visibility, just keep going until you run out of up! Few summits are without a path, where there are false summits you can reasonably expect the true summit to be marked in some way so follow the path until you come to a marker, a trig point, a cairn, a shelter, a monument or a spread of rubbish!
It is safe to ignore advice about a GPS, this gadget has been about for a mere fraction of the time that people have been going to the hills for pleasure, OFs like me learned to read maps and navigate by compass, this has worked for generations and is not dependant on batteries not running flat, LCD displays not freezing up or some military b****r not switching off the satellite to make a training session harder! Don’t get me wrong, they are a convenience but might be so convenient that you will find yourself literally lost without them!
If you are not already trained in the use of map and compass, buy OS Landranger sheet 191, Okehampton & north Dartmoor, study the route to G/DC-001 High Wilhays and navigate yourself to it one fine day - you can get a basic but quite serviceable compass from Poundland. Don’t look up, say “there it is” and head for it, but do it from the map, take bearings, treat it as a navigation exercise followed by an activation and a welcome 4 points. The village of Belstone is already 302 metres ASL so you are in effect starting halfway up! Do this successfully and you are ready for virtually any summit in England, confidence will come from meticulous preparation by studying the map and the resources on the summit page followed by successful climbs.