1. Polyamory is a natural emotion...but it is unacceptable, and your protagonist is just confused.
2. Regardless of what genre you're writing, the core plot point of your story must be your love triangle.
3. One of the protagonist's love interests must treat her like a piece of meat. He is the "bad boy" or sleaze. The other one must treat her like a delicate flower. He is the "good guy" or cheese ball.
4. Remember that your story is about soul mates. So while you want to make it seem as though the protagonist could end up with either guy, one of them is forever, and the other is just kidding himself.
5. Love triangles can not be fixed with a threesome because each party is just too possessive. Also, it's just...immoral!
6. Both love interests must be exceptionally attractive. I did mention it had to be plausible that she could end up with either of them, right?
7. Your love triangle is the key tool to manipulate your readers and invoke feelings toward your story. Think of it as a game of ping-pong, where the ball is just a tight wad of sexual tension.
8. The protagonist has several other pursuers who are interested in her, but don't make the cut. They are like training wheels bouncing clumsily down a hill in wake of the speeding bicycle.
9. Both love interests must have stunning eyes. For example, one might have "cold and mysterious grey eyes" while the other might have "dazzling blue." If you're writing a fantasy, one man might have "deep green eyes with golden flecks" while the others are "violet rainbow supreme."
10. As long as you have an indecisive protagonist, and love interests which are polar opposites and despise one another, the steps to a successful and manipulative love triangle can be applied to any gender or sexual preference.
So there you have it. The backbone to a best-selling trilogy of tactical torment.