A: Most players prefer their delay after their overdrive or distortion. The problem with placing a delay before a dirt/gain pedal is that distortion and overdrive tend to compress the signal to one extent or another, which makes the delay repeats sound louder (and distorted) just like the original notes; this often results in a muddy messy. Running the delay after the overdrive is cleaner, since the delay repeats are based off the already-distorted notes.
Having said all that, try it both ways! You won’t hurt anything, and you may find that for your style the delay in front of the overdrive works great.