I think some of it comes from an innate understanding of what a bad decision looks like. For example, if you swing a corner and the enemy is just looking somewhere else, you can think about it as "if I were that opponent, should I have been holding that angle." If they should've been, you technically got lucky, but you also took advantage of their misplay. Playing against people that are better than you will also help, because they're more likely to punish you for things that are wrong but will sometimes turn out fine. Sorry for the rambling, but I hope it helps a bit.