If you’re wanting to paint neatly up to an edge, say the side of a vase or tree trunk, painting away from that edge or imaginary line rather than towards it is easier. You position the brush at the exactly the right point when you start, then move the brush away from the edge. If you’re painting towards it, you have to decide when it’s time to stop. Lift the brush too early and there’s a gap; leave it too late and you go over the edge.
This short video demo was done with a flat brush and watercolour, but it applies to all brush shapes: