Generally I do a lot of things to try to take my mind off things, sometimes I draw, sometimes I play video games which are good because they are absorbing, maybe have a cup of tea or eat something nice, call a friend to talk about stuff and joke about or excuse myself to scroll through the cat videos on youtube for hours on end.
In general if you are feeling sad I would advise keeping active, getting up at a reasonable hour, having a calm morning and making sure you're showered dressed and ready to face the day puts you in a better mindset than lying about all day. Start taking walks if you don't already, it helps your mind rest and the exercise is good for you! Try to keep active, make sure you make time to go out with friends or simply run errands because sitting about alone can get very bad for your health. Try to eat well with vegetables and fruit and make sure you also have enough to drink and of course try to get a little more sleep by going to bed a little earlier. About 8 hours is a good goal, especially if you are usually a night owl. They seem silly but keeping healthy can to wonders for how you feel too.
But perhaps most importantly of all if you really feel sad you should tell someone about it, maybe you just need to talk to a good friend to get it off your chest, a parent or guardian who can maybe give you more practical advise and don't feel bad about maybe even going to see a professional. If you are really, really down it's far better to go and actually get some help to work through stuff even though it can be scary. But honestly I think the fact you asked for advice is a good step to feeling better! 8D
But I'm just a simple gal on the internet so for a quick fix for the time being here's a video of some sugar gliders that I think are super cute: https://www.youtube.com/watch?v=7ys8N4icLsY
Feel better soon ok!! <3 ^^