You could simply look this up on the internet, but for those of us who are exceptionally lazy, here goes:
Every now and then, say every hour, or whenever you think of it, look around you. Try to check if what you see is real. Are things floating around and is gravity not working as expected? When you look over your shoulder and back, did the room change color, and did the table just turn into a tree? Try to touch something with your hand. Do you not feel any resistance when your hand drops through the couch? If so, you are probably dreaming.
Every now and then, say every hour, or whenever you think of it, look around you. Try to check if what you see is real. Are things floating around and is gravity not working as expected? When you look over your shoulder and back, did the room change color, and did the table just turn into a tree? Try to touch something with your hand. Do you not feel any resistance when your hand drops through the couch? If so, you are probably dreaming.