No cliche's is the first thing. There are almost rare love triangle stories which are original and good. I think a constant smooth flow and twists within a love triangle is one to think about.
There are two types of love triangles: The Normal and the Odd. The normal is the original plot, one chasing after the other whilst the other chases after another. The Odd however could be put psychologically, like, 'the person is mentally demented and so what the person thinks is real (love) it's not.' I'd brag on about this and give ideas, but I hope this is enough for a starter. ;) Good luck on your fanfic!