As long as you keep comparing yourself to others, stalking them on facebook for signs they’re doing better than you, hating on them when they are, gossiping with people and then worrying if they gossip about you, and defining your worth in terms of how many friends/boyfriends/achievements/admirers you have, you will be unhappy.

You know that these behaviours and thought patterns aren’t helping you. So stop.

No, seriously, just stop. It’s not easy, but it is simple. You ask how to begin a practice that will help you be happy. It’s simple. Be happy. Do the opposite of what you describe yourself doing here.

When you find yourself comparing to others, tell yourself: hey, it doesn’t matter what they get up to. I’ll just worry about my own business. And then you turn to your own next step or favourite project and get stuck in that.
When you find yourself on facebook, tell yourself: hey, look, I’m on facebook again. I know that’s not making me happy, so I’m going to go somewhere else now.
When you find yourself hating on others, turn it around: hey now, self, that’s not a nice thing to think. Whatever good and bad qualities they have, I hope they’re happy with their boyfriend/vacation/stylish new skirt/job prospect/gold medal/new position as president of the united states. We all have good and bad qualities, and we all hope to be happy. So I hope they will be happy, and I hope I will be happy too.
When you find yourself gossiping, change the subject: but enough about that person, what do you think of the situation in Ferguson? Isn’t it crazy?
When you find yourself putting yourself down, try practicing the opposite: I may not have a boyfriend, but I have me. I have my mind, I have my plans, I have my hopes and dreams (and if you haven’t, time to get some!) I really hope I’ll do well and grow happy. I don’t know if all these cheesy lines are going to help with that at all, but I’m willing to give it a shot because being unhappy is just no fun!

Or just, you know, keep a gratitude diary or something. Any little step can be the first one.

I’m not sure if this is helpful, or if it’ll just annoy you. I do know that there are things you can do to change the way you think and act, and through that, change how happy you are. I managed it. So have some others on this forum. It’s a long road, but the weather gets better as you walk along.