20 week scan. Info?

I have my 20 week scan this coming Wednesday and we really want to find out the gender. I was wondering what tips and tricks you used if your baby was facing backwards or had legs crossed. I heard about drinking orange juice but when should I do so? I will already be filled with 1L of water so should I just bring an OJ bottle with me and if they can't see anything drink it or drink it a certain time before my scan?