Look through previous dreams in your Dream Journal.
If you start to notice patterns in your dreams, you will notice dream-signs, or certain things that continue to reappear in your dreams. This may be as basic as all dreams are in your backyard, or all your dreams have fans in them. Get into the habit of doing dream checks every time you see your dream sign, and eventually you'll see your dream sign IN a dream, do a check and realize you're dreaming.