If I was buying I'd look at things like

Spaciousness... so de-clutter and make things look as white and bright and big as possible. I would remove the posters coz it would make rooms look smaller. If you have tiles on the floors and rugs, it might even help to roll them up.

Cupboard space - so make them tidy

Clean - Coz you get whatever mess/dirt/dust someone else leaves behind and it's not appealing to many!

Nice Gardens - I love gardening so I'd look at how big and neat the garden is. Although in saying that our house in Perth was a total mess when we bought it, but we used that as a reason to buy it so we could put our own stamp on it.

I look at the layout of the house, but there isn't much you can do about that. Some places you like, and some you don't.

Maybe put some fresh flowers in the house....it might give people the sneezes, but they are always so appealing!

Good luck and stay positive