DON'T! Seriously it's really not a good idea.
I KNOW people do it, or have tried it and I've heard all of the horror stories and even cleaned up a few failed at home attempts.
Here are most of the reasons NOT to try this at home.
1. Unless you are a contortionist you'll give yourself a migraine trying to reach everything.
2. Unless you live in a house of mirrors, it's going to be very hard to see all the places where the hair is hiding.
3. Unless you have four hands you'll never be able to hold the skin tight enough. This is really the biggest reason NOT TO WAX YOURSELF. If you can't keep the skin tight, you won't get a good application of wax. If you don't get a good application of wax, you'll break hair, leave hair behind and in general not have a satisfactory result.
4. The four hands thing again. If you can't hold the skin tight enough on removal, especially in the labia, you risk lifting skin or worse yet tearing the delicate labia skin. So instead of a trip to the spa to pay a professional to do it for you, you'll be making a trip to the ER to get stitches.
5. Once you apply the wax you MUST remove it. That means you can't loose your nerve and not remove it. Oh and soaking in a tub of hot water DOES NOT REMOVE WAX, it just makes sticky things stickier.
6. If you have thick, coarse, dense hair, you are asking for trouble trying to do your own Brazilian, you're more likely to end up with a garden of ingrowns and stubble and that's no fun.
Though there is humor in the delivery, I hope you understand the seriousness of the message. The Brazilian is a waxing service with a high degree of difficulty and as such requires a high degree of skill to perform efficiently, proficiently and effectively.
Bottom line, if you MUST get a Brazilian go to a pro.