actually i have done a lot of research on this subject because i thought it would be a really fun thing to do.
Basically what i found out is that you have to keep a log of your dreams because you have to be able to recall your dreams or you won't be able to remember if you had a lucid dream or not.
One strategy that made the most sense to me was writing something on your hand like a D, then constantly check it throughout the day so it becomes a habit, then once in your dream you might check it and it will be a different letter or it might be blurred hence you know you are dreaming.