depends on how old.
Condition of wiring, any recent works done that are certificated.
Likewise with the gas, ask to see copies of Corgi certificates.
Go around the rooms and look for damp or nasty smells.
Look up on the roof for signs of tiles loose or new tiles that may have been replaced.
Look at outside drains for "green mold" that indicates breaks in the pipes.
If double glazed look around the frames inside and out, look for any "clouding" on windows which might indicate a damaged unit.
Go up into the loft with a torch and a good nose.
All the usual stuff I suppose.