A trick that has worked for me: pull on a finger. In a dream (probably because I've conditioned myself) it will stretch like taffy which was enough to indicate that I'm dreaming.
Interestingly, after a while seeing my finger stretch wasn't enough to convince me that I was dreaming: I would question whether it was stretching enough. Like "oh, it's only double it's normal length, so this is probably reality." This has also happened with other tricks I've tried, like try to fly ("I'm only hovering; probably not a dream"). It's almost like you build a tolerance for particular abnormalities.
Sorry, that was longer than I meant for it to be
https://en.m.wikipedia.org/wiki/Durum_wheat