It starts with self acceptance. Some people hate themselves and have a constant negative internal dialogue that is constantly criticising everything about themselves from looks to actions to feelings. A good start to loving yourself is to turn that off and replace it with a self positive and self appreciating outlook and dialogue.
We all know people who "love themselves" in a very vain and self important way, and I imagine that is not what your friend is suggesting. Would you talk to a person you love the way you talk to yourself? Would you criticise the way they look, the things they do or say, the way you do to yourself? Accepting yourself the way you do people you love, I believe, is the way towards changing your internal conversation and reevaluating how you feel about yourself.
When you feel positive about yourself, accepting whilst acknowledging your flaws and failings, you can accomplish so much more. People who loathe and hate themselves are trapped in a cage of self abuse that is largely of their own making. Letting yourself free of negative, self critical, self defeating thoughts and building a positive replacement is how to start loving yourself.
