Lists, lists, lists. Go room by room, listing everything that would make it nice/cosy/homey/however you want it to feel: hang pictures, hang curtains (sub list: squire curtain pole, put up curtain pole, make curtains, buy hooks), bookshelves (measure up, get wood, fit shelves to wall, stain and varnish, etc), lamps, rug, rearrange furniture, paint, etc.
Then take that list and rearrange it into types of task: painting, drilling, organising/decluttering, acquiring items, making something. That way when you get out, say, the drill, screws and rawlplugs to do one thing on the list you can blitz through a few items at once. Same with painting, decluttering, picture hanging: you can do a few bits at a time.
Some rooms will start to come together more quickly than others, at which point you temporarily abandon method 2, doing things via task, and return to method 1, and see what you need to finish the room and how you can do it.
This also all has the bonus of being ridiculously satisfying for crossing things off – I keep my lists on the fridge and most lunchtimes thanks to WFH I can do a task or two. (Today I hung a picture and did a bit of gardening.) Every now and then I take a couple of days off work and just power through stuff; not being able to go anywhere or have holidays helps enormously!