I agree with anything not used within the last 12 months - toss it and anything not used in last 6 months - pack it.
Linen - I keep out two sets. Just in case you can't get one dry.
Toys - you'd be surprised with how little they can manage on. At the very least get yourself some plastic tubs with lids that can be stacked neatly in a wardrobe and only keep a few faves out.
Definitely all seasonal things can be packed away. Wardrobes that aren't over flowing def look more spacious.

Be careful with aromas in the home. If it's a new house I would stick to just fresh air. If it's older and needs 'homeying' then avoid strong smells as you never know who is going to look though your house and what they're going to be put off by. For example I do not likes smells hanging around of any sort - baking bread or anything cooking/strong oils etc would make me suss that they were trying to cover up another smell, be it animals or smoke or whatever.
For open homes remove all signs of your animals inside. Many people don't like animals inside and will def be put off by that.
Beds made within an inch of their lives, few family photos, very little clutter on surfaces.
Get in and give the house the best clean you've ever given it and then I know it's hard but maintain it. Dirt is def off putting to buyers.
Get rid of junk/clutter from the yard.