The SM57,
my own opinions:
A wonderful little mic, hasn't changed in decades. Awesome when used properly on snare drum, brass instruments and guitar cabs. Also a great all purpose dynamic mic, but it needs more taming and caressing than the SM58 I find, especially if daring to employ with vocals.
It has a stronger presence peak. As in, it is designed to pick up frequencies in the mid area more than the highs and lows. This is one of the reasons it is awesome for a snare and brass. It also has a prominent "Proximity effect". The closer you get the warmer and fuller the sound. However it has an open diaphragm, so popping will be a bigger issue as you get nearer. Vocal wind blowing onto the mic from p's and b's, also know as "plosives", are a big concern here.
My advice to start with: Forget the external things. They are cardioid and pick up sound mostly from the front. So don't worry about foam etc. Find a room that is dead or has a nice ambience and set up central.
SOUL/BIG VOICE: I have recorded these dead on, at a distance of a meter of more. Kind of treating the vocalist like a brass instrument. This relies on the vocalist singing BIG to compensate for the distance. You won't get a close feel (naturally) but it will work with the right singer
POP/STANDARD-TO-QUIET singers: Firstly, treat the singer a bit like a guitar cab. Turn the mic 30-45% off centre, left or right, NOT up or down. Then place a decent pop shield over the mic, perhaps an inch or even less away from the mic head, so the singer is performing towards the SIDE of the mic head slightly. This seems to warm the sound as the mid-heaviness of the vocal is lessened. It also serves to reduce issues with pops.
Let me know if this helps