When I'm down, I sit down and think about my future.
I really don't have any friends in Minerealm because people find me arrogant, selfish, and annoying

.
It's okay if there is no one to cheer you up.
What I do if I ever do get sad and lonely, I just imagine me in the future talking to me in the present.
I always imagine me in the future as a great person, and that person can cheer me up and give me hope on fulfilling whatever goal or dream I want.
For example: (One of my imaginations that I have when I feel down)
Me in the future: Hey, what's up Romel?
Me in the present: You know, just feeling down, thinking about me and why I have no friends...
Me in the future: Don't you ever think that, you have me as a friend, and I will always be your friend.
One day, you will become like me; rich, intelligent, and best of all, I have friends.
Me in the present: Well, how do you expect me to turn into you?
Me in the future: You are me, but being in a bad mood won't help.
Just remember this, don't let friends get in your way of fulfilling your life.
They will want you in the future, because you have accomplished your goals...
There was my imagination example, and yes, I did have that before.
It does happen to me alot too. :'/
Anyways, if that doesn't work for you, or you don't have a very good imagination, I have another method of keeping you up.
When you are down, it may mean because you are stressed out by something.
It is always a great idea to relax yourself and keep your thoughts into the good things and away from the bad things.
You could do this by exercising, it will focus your mind more into keeping you healthy, thus, keeping you away from sad thoughts.
You could also do this by being more social with your family.
If there is something you need, you could always rely on your family.
Talk to them or play with them.
They are there for you for a reason.
Lastly, the method I use for keeping me up when I'm down is giving your pet affection.
They can always relieve stress, and I think it's the best and easiest way of doing it too.
Those are my ways of keeping my thoughts away from sad things.
I hope that they have helped you in any sort of way.
tl;dr
Keep sad thoughts away by ignoring things that get in your way of success.