normally, people place any dirt or compressor effects before modulation. the idea is to compress/boost the tone, before actually modulating it. however there's nothing wrong if you want to explore new sounds and whatnot
only thing i know is placing a flanger before your distort will create a distorted air plane lifting off sound somewhere along the sustain. but it'll sound somewhat dirtier.
*edit* experiment and see which is a better choice for your guitar voicing...