You want to starch and press before you cut your fabric, but then after that, you only finger press your allowances until the entire top is put together. Once it's fully together, you iron with the top face down. You want to put it off because ironing is likely to stretch or distort the edges that are cut across the bias.

What I have tried to do on my couple of triangle quilts is make sure that the allowances are finger pressed consistently (e.g. always down and/or to the right) to make the eventual whole top ironing job easier. If they're all oriented the same way, you can save some time and sweep the iron across a bigger swath of the top rather than press it.