When I'm feeling sad, self care is very important. I paint my nails, get some nice face and hair masks. Watching happy movies and doing arts and crafts also helps, but it's important not to shut yourself at home. Find a good book and go to your local coffee shop.
It might sound weird but don't be lazy. All the things that you want to do for yourself, don't put them away for tomorrow. Love yourself, and do them today for yourself.