Depends on the market in your area, we asked our estate agent for advice, they were helpful guiding us on expectations of our likely buyers in our price bracket (first time buy or lower budget end of the family market in our case). We were suggested to leave our tiny box third bedroom as a study for example, to appeal to the young prof market, which was a surprise as we had planned to borrow a bed to market the property. (The tactic worked as our buyer wanted to use it as a dressing room for her clothes)
Don't paint unless it's a crazy colour, but clean marks where possible and do an obvious repairs like filling holes/cracks in the wall (non structural stuff, we weren't trying to cover anything up!)
We took away any photos that had us in, and replaced with some landscape ones in the same frames. We also kept a few ornaments, candle holders etc. Removed half our books from bookcase and styled and arranged by size. Took all the photos/notes off the pin board and fridge in our kitchen and replaced with a few 'art' postcards we had from IKEA.
We kept a few children toys in a storage unit in the lounge, but shoved most into our cars for photos and viewings (the jumperoo!)
Outside we put colourful planters at the front door and gave our front and back yards a good tidy up with garden furniture out.