although slack has really said it all...i suggest/do:
first get the amp to sound the best that it possibly can...and yet back up on the distortion a tiny bit when you record it.
second, find the perfect mic spot...play around until you think it sounds player as hell...i mean really player...haha
you'll notice that if you start with you SM57 pointed dead center at the cone, maybe 2 inches away frlom the cloth, that if you even move it an inch or 2 to the left, the sound may change dramatically. so be carefull, and take your time.
lastly - i record tons of guitar tracks. sometimes even 6 of the same thing. 4 on one guitar setting, 2 on a similar, but different guitar sound setting.......
then, i usually pan something like (l/r) 80/80, 40/40, 15/15...or something like that..just depending on the individual mix.
that will generally give you a hell of a thick guitar sound, which i love. stuff like Weezer blue and Poison the Well - Opposite of December...the REALLY thick stuff.
honestly, i found one of the fullest kick/guitar/bass mixes in Poison the Well - Opposite of December............although i'm sure its nobody here's favorite style, lookit up on kazaa, i think you'll love the mixes.