fuzz factory is a sensitive pedal. The best effect i gotten i out it, is to have it directly after geetar. Where the volume pot/tone on geetar can have bigger effect to manipulate the squealing and temperament of the pedal.
If theres a need to put any pedal before the FF, it will be better to have one with true bypass/bufferless. The sound of the FF can get affected with some buffered pedals before it. I didnt like the way it sounded or changed in sound plus the way it react with the pots on geetar. If wanna put pedal between the geetar and FF, best to try it with own setup and listen to how the FF reacted, with a preferred setting, then change it to geetar and just FF for comparison.
As for the placement, before or after, that one, if wanna be "text correct", then put modulation all the way at the back.
If wanna think which one is the best, then think in the line of, for example, whammy, phasor, delay.
Do i want to whammy my distorted sound/clean sound then send it to phasor
or
Do i want to phase my distorted sound/clean sound then send it to be "whammified"
or
Do i want my delay to affect every other effect in the chain or phaser to affect averything in the chain
and so on....
Before after, what goes in, what comes next. When you play around with the sequence of modulation effect, you will hear differences, what these are, will become your preference of sound with what you have/playing with and the fun in mixing and matching.
Theres is nothing experimental in it btw, its just a matter of finding out the "best arrangement with what i have and preferred way of making it sounds the way i like"