Check the windows to see if they have a draught, or if the wood is rotting underneath the paint, if they are wooden.
Look under rugs, unless you are planning to replace the carpet anyway. I suggest you do - other peoples furniture marks make it look awful anyway.
If the kitchen isn't ideal, try and imagine if you could make it ideal. If you want an island or something, you'll never be able to have it in a long thin kitchen, which may seem obvious of course. But what I'm saying is don't just think "oh, we can change the kitchen', try and think about how you'd like to change it and whether you could achieve your ideal.
Think about what walls you could knock down if you were to want to go open plan.
Is there a downstairs cupboard for brooms and hoovers? Is it possible to not have your washing machine in the middle of the kitchen? Is there room for a dishwasher? Basically, can you accommodate things you might want, even if they are not there now? Is the fact they are not there now for a reason?
Parking. It will drive you mad having to move your car to let your OH out. So you will park on the street to avoid it. So will everyone else. Or perhaps there is no off road parking. Fine, but what time if the viewing? If it's the middle of the day when everyone is at work, come back in the evening and see what the parking is like.
If there is no shower in the main bathroom, is it easy enough to stick a temporary one on the wall via the tap, or is the tap at the wrong end to be able to do that? Will it mean a whole new bathroom if you don't want guests traipsing in your ensuite?
Look out for house viewing mode tricks. No bin in the kitchen, no TV in the living room, no wardrobe in the bedroom. Can make it look spacious for viewing but make sure everything you need in the room is already there, if it's not a massive house.
Try and look out windows into the back yard next door to get a feel for who your neighbours might be. Is someone standing there smoking near the window you might want open in the summer? Is there a filthy old mattress and a burnt out car and a chained up barking dogin the backyard? This can give you a bit of insight into what kind of lifestyle your neighbours might lead, at the risk of sounding judgmental. One person's idea of a trampoline and a football net as being a nice child friendly neighbourhood can be another person's idea of suburban hell.
Obviously a surveyor will pick up on really important structural stuff.
But if you are thinking of making an offer, don't hesitate to do drive by's at various times of day. Around school drop off time if it's near a school, 8pm when most people are home, that kind of thing, to see if it drastically changes.