How do I learn loving-kindness meditation properly?

By moving through the circles in order rather than jumping to the hardest one. The traditional sequence is yourself, a benefactor, a dear friend, someone neutral, someone difficult, and then all beings, and each stage is easier once the one before it is familiar. Not feeling much at first is ordinary rather than a sign it is failing. In StillMind a Loving-kindness course paces those circles across 3, 6 or 8 sessions: the longest gives each circle room of its own, while a short one keeps the pillars of self, the difficult person and all beings and leaves the middle circles for another course. If being kind to yourself is the hardest part, it can open on a benefactor instead and come back to you once the practice has steadied.