I deal with clinical depression and have a lot of time where I just feel awful.
The number one thing I can suggest is NEVER become cynical about it. If you become a hateful asshole, you end up dragging down everyone around you and you are more or less digging your own hole of despair. Try to avoid jealousy. Try not to approach people with different views in a hateful manner. Some people might have awful views, don't feed their hate, but wish upon them that they weren't so full of hate.
Similarly, you should not obsess over past "regrets". Yeah, shit happens, and what is done is done. Instead you need to learn from your mistakes and use that to move forward and improve yourself.
It is also good to have hobbies or something you just enjoy that helps relax you when you are stressed. Have a social life beyond just chatting with people online.
But sometimes at the end of the day, you might need professional help. Like talking to a therapist and such.