Bodybuilding?

Eat like a pig, shoot steroids and every now and then go to the gym and lift.

I'm a competitive bodybuilder (natural and tested). You don't need steroids.

There are 4 different categories for women in the bodybuilding world. Bodybuilder, Physique, Figure, Bikini. It's a good idea to understand the differences between them and work towards one, but you may find as you train that your structure or mass are more suited for a different category.
myfitnesspal.com/blog/usmcmp/view/bodybuilding-vs-figure-vs-bikini-686680

A good idea would be to find a personal trainer who has competitive clients in at least one of the categories. They'll be able to tell you about how long you should build and how long you'll need to cut before you should take the stage. Many women want to compete as soon as possible, but most of us need a year or two to grow before our first show.

If you can't find or afford a trainer then start saving for one (as well as for the costs of a show). Begin a hypertrophy routine (like Layne Norton's PHAT program if you are an experienced lifter or HST if you aren't as experienced). I can't give you much more general advice, because after this it becomes more personalized and specific for where you are at. Feel free to send me a message and I'll do what I can to help get you on the right path.