Loving other people is simple in comparison. You know your every flaw, every mistake, every thought, every action. No love is more difficult or more rewarding than loving yourself.
If you love yourself, if you're made of love, if you are love, only then are you able to love others wholly and completely.
Loving one another is important, certainly. I feel like this gets covered pretty well in our culture. From a young age, this is the mantra taught to many of us: Love one another.
When I say my affirmations with myself in the mirror every morning, after I've quoted the character Yul Brenner's "I see pride" affirmation from Cool Runnings, the very last words I leave myself with are: "I love you."
If you want to change the world, change yourself.
If you want to love the world, love yourself.