Well, start by putting the highs on a track and the lows on a different track.
If the vocalist has Suicide Silence kind of highs, with some screechy gurgle, I over-compress them (don't get too carried away). It smooths the "liquid" sound out by overdriving it without distorting it. Any other kind of high I compress it "appropriately." DEFINITELY high pass and looking around 1.2-4.0 kHz to boost if it isn't standing out. Think about De-Essing too.
Lows in amateur vocalists tend to blow. Due to them being much more quiet (usually) than highs, nothing is pushed as hard so I tend to compress the .... out of them. You'll find that this levels everything out to a single dynamic. Downsides? No dynamics. Well, goodie, most vocalists aren't good enough to create dynamics anyway so who cares. You can do all your "dynamics" with automation. EQ is trickier here. Is he a dumb asshole who cups? You need to look and cut out mud in the high lows and low mids (still high pass this, you should all the time usually). If he doesn't, it depends where his lows sit, but generally you're looking in the same place as the highs.
If you want em bigger, try parallel compression.
Keep in mind, this is just my amateur experience. I just know what works for me!