I still do not agree with everything that has been said here, but some more tips are too:
-High pass at around 60-120 hz, use your ears. This is to make room for the bass and kick.
-Low pass at 8000-14000 khz, use your ears. This is to cut junk frequencies. I have heard many people low pass at 7k, with great results.
-Also, bypass the cabinet in metal amp room, and load some cabinet impulses. Guaranteed better sound. Or even look into some of the best freeware amp sims, such as LePou and TSE. I prefer free plugins when dealing with high gain tones then commercial to be honest.
-I also like using a saturator when using amp sims. They make the guitars IMO sound thicker. There are some great free ones, but
this one is known to be great.
-I tend to not use a compressor on my guitars, but I know many do and achieve great results.
-IMO, always use a tube screamer simulation with amp sims or the real thing when recording real amps (if they are tube, never on a solid state amp). Look into BTE Audio's free screamer plugin, or Mokafix's commercial Creamtube plugin.