My favorite reality check is number 11 on that list I linked to, the breathing test, where you close our mouth, pinch your nose shut, and try to breathe, and if you can still breathe, you know you're dreaming. This one works very well for most people, and the only way I've ever known it to not work is when for some reason, you can't do it right, and that in itself is a sign that you're dreaming.

What seems to be the second most popular and reliable is the first check on that list, the clock test, where you look at a clock (preferably digital) , look away, then look back. If what it shows you doesn't make sense, or it changes unusually between the two times you look at it, then you know you're dreaming.

Those two checks, or possibly even only one (I only ever use the breathing test) should work pretty well. If you want to try more, I also suggest seeing if light switches work, looking at your hands to see if they look normal and have the right number of fingers, or trying to stick one of your fingers through your hand, as all are popular and fairly reliable reality checks.