At the risk of sounding cliché, think nice of yourself and truly feel it. You don't have to think you're awesome or even 'love' yourself, just find things you like about yourself, praise yourself for being that way and feel the pride it gives you. Don't even mention these things in conversation, just think them and feel them. This might need some self-revelation that takes effort and time, but once you think of yourself as being a nice being you don't have to prove anything to yourself (or others) anymore. You won't feel the urge to make the best joke of the evening anymore (often failing and make others think you're awkward). You won't be crippled by the fear of rejection (leaving you standing in the corner looking jealously at how others succeed so seemingly easily in social conversation). You will not try so hard to be liked anymore, because you already are, by yourself. You will finally be able to see that you are a nice person and it will show others that same image, a likeable person. Now who doesn't enjoy a conversation with a nice person? With all these needs to prove yourself out of the way, you will have more time to be genuinely interested in the other, making you an even nicer conversational partner. Also, outside all social stuff it makes your life a lot nicer. Be sure, it might take a lot of effort and time to truly feel this way (and not just superficially think it), but once you find pride in who you are, everything will get easier.

Oh and don't give me that non sense of 'but I am unlikable! There's nothing good about me.' False. If you think that way, it shows that you're capable of empathy and that you are caring. Truly unlikeable people are not capable of these thoughts. Worst case, you haven't found good ways to show your good sides, which is exactly what you will find when you can truly say: "I like myself."

source: been awkward for almost all my life, got into a few personal problems and have been working on myself for about a year now. I'm far away of being finished (if you can ever be), but everything I gained is already worth the trouble.