A little counter-intuitively, meditation seems easier if I have some mild discomfort, like an itchy skin, feeling slightly ill from having strong tea on an empty stomach, or an excess awareness of saliva secreting in my mouth. My attention keeps getting automatically drawn to these discomforts, so I can use them as an extra meditation focus in addition to my breath. Over time (several sits) it may become harder to use them as foci, though, as they stop feeling uncomfortable.

Headaches work for me. There are also some types of strong negative emotions which improve my meditation enormously, while others prevent meditation from working.