So much of it is to do with your breathing, Learn to become more aware of it, and work on keeping it relaxed as you get to the edge. If you start holding your breath it’s likely to push you over. Beyond that, it’s a case of practising and learning to touch your clit very gently just to keep yourself on the edge.
Often when people talk about this they actually mean they get to the edge then slip off a little and get back to it, and that’s totally okay! But often as you practise more you’ll get better at just floating along in that amazing ‘edgespace’.
Also, as you practise, don’t be too worried about slipping over the edge, it’s fine, you’ll mess up sometimes when practising. Obviously, you ruin the orgasm, so as soon as you go over, you stop any stimulation. But then you’ll find you are still as horny as ever and you can resume edging pretty quickly.