Okay got my first blockage last night. A bit cheesed off about it as it was six hours into a seven hour print.
The machine started to make a ticking noise and after a few minutes (couldn't see anything obviously wrong so I let it keep going) I could see the nozzle wasn't very close to the object and the heat from it was just roughing up the surface.

Any tips on how to clear the blockage before I start?