What works for me is recognizing what my dream signs are. It doesn't generally have to be all of them, because I have many But I do generally tend to dream about certain things for a period of time (like right now, dinner parties/manager's meetings are a big thing for me). So when I see those in real life, I check to them.

Essentially, a good reality check comes from within. Remembering to remember is often the term that gets associated with prospective memory. You can either choose one of your current dream signs (you should be fairly familiar with them if you keep a dream journal), but if you can't recall any at the moment, then you can just choose a sign. It could be anything like, seeing a person with long hair; looking in the mirror; signing your name (or just writing something down, to be more vague); pressing buttons, etc. Dream signs can literally be anything. Pick something and remind yourself at the start of your day that when you recognize your dream sign, that you will remember to think about dreaming, and thus, reality check!