on a little walk if you have the time. if you work from home, or you're just at home all day normally, go for a walk for an hour, give yourself a lunch break and see the outside. i know it's so cold at the moment so it might not appeal to you, but wrap up warm because it's not healthy for you to be locked up inside all day. i know for some it can be so hard to leave the house, so if that's the case, i'd recommend opening your curtains, opening the window and letting some of that fresh air inside.
these are my tips, i hope you 