Assuming that you have at-least a vague idea of where you are, start by aiming for a good line feature - a motorway or major river for preference. Make sure that at the most "lost" you could be, you'll definitely be a known side of some point feature on that line feature.
Then turn towards it, fly till you get there, and you know exactly where you are.
For example, if you are in Kent, head North until you get to the Thames, then turn left until you hit the Dartmouth crossing. Whilst en-route, plan how you're going to get where you need to be from there.
But try and do it without infringing airspace. So, for example, if you are somewhere NW of London, you'd be better heading SW for the Thames than SE for the M25 which may cause offence, and do it above 3500 ft so you shouldn't hit any ATZ/MATZ. In that case, once you'd hit the Thames, you'd be better turning right for Oxford than Left for Reading since latter would take you into LTMA.
Better still don't get lost, but any pilot who tells you he's never done that is lying.
G