Your song needs to be from this year. Maybe you like retro clubs and like to be a hipster that listed to classic rock, but in order to be trendy and fluid at modern clubs you'll need to work with something more modern.
It needs to be sung by a girl. You are not some masculine, chiseled baritone - you are a sissy girl and you're going to practice singing like a girl. Girly lyrics are a definite plus; referring to yourself as a girl or queen in song will always help in the long-term.
Lastly it needs to be upbeat, with a fast tempo. Something you can move and dance to. None of that shuffling shit. Get down, swing your ass and move your arms (with the rhythm, obviously).
If you're not up on modern hits and pop music you can always try one of these:
Love on Top - Beyonce
Call me Maybe - Carly Rae Jepsen
Bad Girls - M.I.A.
And then you're going to practice singing the song you pick at least once per day (as feminine-sounding as you can - I expect progressive improvement). You'll also dance to it, but you're also going to dance to other songs as well -- at least 15 minutes of sexy, sensual dancing in rhythm with the music you choose. You can start by watching videos (you don't need to stick with modern music for practicing dancing Britney Spears, Beyonce, Shakira and many others are good places to start, whether or not you like the music). But you will dance and practice what you see.
I expect you to work at this and become a passable dancer for cheering on your favorite athlete(s) in the last day of the Olympics, but you're going to keep practicing with new songs and new dances. Clubbing and dancing is the favorite weekend activity of many young women, so it's time you learned how much you love it too (the fact that it will help you get fit, move more sensually and maybe act a bit sluttier is just a bonus).
This is an excellent starting step to get you outside, confident enough to dance and hangout in front of other people. Now get out there and start shaking that moneymaker, sissy.