You need to change your mindset. I know that is easier said than done, and alas there really is no method that you can memorize, no trick that will get you to do it. What you need to be able to do is to tell yourself "This could be a dream." And you need to be able to believe it. Because if you do not believe that this could be a dream right now, you are not going to believe it in a dream either, and you will be wrong, but you will not be able to be convinced because you will not trust that this could be a dream.

It does not come natural to us to question reality. Our natural mindset is to always believe that whatever we experience is real. And that includes flying elephants when we encounter them. Our natural tendency not to question reality is so strong that we will look at those flying elephants and rationalize them: the circus must be in town, oh my gosh I am going to be famous if only I can get a photo of those flying elephants and get it authenticated then everyone will know that I am the first human to ever see a flying elephant, etc. Our mind will use whatever rationalization it can to hold on to the illusion that it is experiencing reality even if it is not. And if we are not willing to believe that this moment right now could be a dream, then how come we believe that the flying elephant is real? After all shouldn't it be much easier to believe that I am dreaming than to believe that elephants can fly? unfortunately, at the time when I encounter the flying elephants my mind may be impaired because it is asleep and thus not fully able to access all logic and reason. So the only way that this impaired mind will be capable of conceiving of the notion that the most logical explanation is that it is a dream is if that thought has occurred to me before in waking life because otherwise it will be a coin toss between what my impaired mind considers more likely: that elephants can fly or that I can be dreaming right now.

So your goal is to change your mindset to increase the odds that your mind will decide that this is a dream is a more likely explanation. How do you convince yourself of this? You know how you believe stuff and become convinced of something better than I do because you know yourself, so surely you can figure out a way to convince yourself.