How do i stay lucid when dreaming?

So, i've been having this problem for a while.
Last night, i knew i was dreaming - in my dream, i was walking in the school's pool room, and there were tables everywhere with people sitting by them, eating lunch.
Now, this is where the problem kicks in (not just specific to this situation) - i got this girl to walk away from her table, and then we began to have sex. Towards the middle, i felt the control just slip away; and then the next thing i knew, i was just having a regular non-LD :( I'm glad i don't wake up anymore (grabbing things/spinning around got me through that), but losing the lucidity is just a pain D:
How do i overcome this?

Every activity, which requires your full attention - including lucid sex - may cause you to lose lucidity. Reason is, that in a lucid, you need to keep all your senses engaged, to be part of the dream, to pay attention to everything around you, to always know that you are dreaming.

And when you are engaged only in one activity, you lose track of where you are, then your dream tends to fade.

Now, this is not a rule set in stone, you still may be able to do it. But don't be surprised if you lose lucidity, or the dream ends all together.


***Moved to Dream Control***