I have several different techniques, but this is my favorite.
I wait until I'm home alone, and go into my bathroom. I begin by thinking about my girlfriend touching my nipples, licking them, and touching me through my panties. As I slide the panties down, I talk dirty to myself. My favorite things to say are things like calling myself a whore, a slut, or something like that. I spank my ass hard a couple times, then grab the toilet brush and my electric toothbrush. I imagine my girlfriends hands running down my body, then I slide a finger between my lips. I think about her giving me a hand job. I ask myself if I am ready for 'the toy,' and I beg to my imaginary girlfriend. I roll over into doggy style position and I slide the toilet brush handle into my pussy. I like to make as much noise as I can, begging and crying out my girlfriend's name. I do not need any lube since my pussy is already so wet that the handle slides in and out. The handle has a larger part at the end that feels amazing as it presses against my g spot. When I am almost about to come, I turn on the electric toothbrush and press it into my clit. I scream and moan as I see my girlfriend's face in my head. When I come, I imagine myself eating her pussy and her screaming.
It's the best orgasm I've ever had. :]