It often helps to keep a dream journal by your bedside to immediately note down anything, even the smallest details, that you can remember right after waking up, alternatively you can use a voice recorder if that's easier. You can also make a habit of seriously checking if you are currently dreaming or not (think of what you were doing before this, see if you can put your hand through a wall or will yourself to levitation etc etc.). By making it a habit you'll end up instinctively doing it when you are actually dreaming. If you're too lazy to do any of that (like me), I've found that setting a clear intention to lucid dream when you're very sleepy and about to go to bed should increase your chances of it occurring, I don't know by how much though.
A more complicated version of this would be: sleeping for 6 hours, waking up and keeping yourself occupied for 3 to 50 minutes, going back to bed but specifically setting the intention to not move or open your eyes the next time you wake up, the next time you "wake up" you may find yourself in a lucid dream or under the near-perfect conditions to leave your body and astral project. This method is taken from a book called "The Phase" by Michael Raduga and is the one I have found the most success in for astral projecting and unintentionally lucid dreaming, though that was a nice experience too. I suggest reading the book because the method is better described there, he pretty much goes right in to detai