Fire is all about combustion.. Just time everything to get the perfect combustion. Jade spirit, your on use trinket, proc trinket. Try getting 4-5 pyros in a row while you have everything up and combust = profit
Some people here underestimate frost tho. It has amazing burst and is the spec to go for some fights. Frost also has a more consistent dps.
Felt like adding.. If you are only throwing a good combustion and you are unlucky till your next combustion it is for sure that you will do less dps as fire than frost.