To get Kelly to lapdance you:
Complete the game.
Load your completed save aboard the Normandy.
Dump whoever you're currently romantically entangled with.
Piss about a bit until you get an ingame e-mail from her.
Head up to the cabin, hit the button next to your computer to call her up.
Enjoy.
Note that you have to A) save her from the Collectors and B) respond flirtatiously whenever stuff comes up. If you've had dinner with her, you're doing well. If not, you're an idiot because she offers to feed your fish for you after you have dinner with her which is a mother-farking blessing.
DragonsAteMyMarbles said:
Flirt with her at every opportunity, and don't romance anyone else. After the suicide mission (assuming it doesn't go... y'know... badly) she'll email you - after that you can hit the intercom in Shepard's room to call her up.
You can romance other people, you just have to break up with them post-game.