There are a lucky few born with natural charisma - masters of working a room in seconds with handshakes and laughs. Candidly, I was not the most likable person in the room during my late teens and early twenties. 
I admired the way likable people made me feel and how others people gravitated toward them. It hit me that our greatest gift is the way we make people feel. I wanted to learn the secrets of their success.
Starting in 2011, I started learning how to be more likable. The most effective thing I did was notice the behaviors and traits of the most likable people - and then adopt them as mine own.
Here's a list of 39 things that the most likable people do on a daily basis - so you can do the same.
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The 39 traits of likable people

  1. They actively listen.
  2. They make a great first impression.
  3. They're accountable for their mistakes.
  4. They do what they say they'll do.
  5. They treat everyone with respect.
  6. They ask questions instead of making assumptions.
  7. They laugh.
  8. They live for themselves, not to please others.
  9. They follow-up.
  10. They smile.
  11. They remember your name.
  12. They offer to help.
  13. They aren't afraid to make mistakes.
  14. They send thank you notes.
  15. They encourage others.
  16. They speak slowly and confidently
  17. They don't judge you.
  18. They apologize.
  19. They forgive, but do not forget.
  20. They don't speak for you.
  21. They know how to give a compliment.
  22. They know how to accept a compliment.
  23. They tell the truth.
  24. They celebrate others.
  25. They have good body language.
  26. They don't criticize others.
  27. They give you their undivided attention.
  28. They don't make you feel defensive.
  29. They don't take credit for other people's success.
  30. They maintain good eye contact.
  31. They let you do most of the talking.
  32. They know how to have a tough conversation.
  33. They admit when they're wrong.
  34. They are consistent.
  35. They don't interrupt.
  36. They're not afraid to be vulnerable.
  37. They don't exaggerate.
  38. They can laugh at themselves.
  39. They're optimistic, without being unrealistic.

This is a way of life

Take notice that these behaviors are all about being a good person and making others feel good. They aren't tactics and tricks. They're a way of life. You will see dramatic change when you make the necessary effort to practice these behaviors and truly adopt them into your daily life.

Putting this into action

Meaningful change is achieved when you consistently make small improvements over time. My results came from focusing on one or two of these behaviors at a time, and practicing them in my interactions until they became a habit. Only then would I move to the next one.
Learning to be likable takes time, self awareness, and practice to authentically mold these behaviors into a natural routine. There are no shortcuts. 

Additional resources

If you don't quite understand these items, then do more research. The two books that helped me the most were "How to Win Friends and Influence People" by Dale Carnegie and "Crucial Conversations" by Al Switzler, Joseph Grenny, Kerry Patterson, and Ron McMillan.