First, try your best to sing properly, of course. If you have to be quiet or very loud, then just do it, because turning up the volume in the mix isn't the same thing as actually singing it that way to begin with. But after you've done your best to sing how you want it, manually adjust the waveform phrase by phrase. Actually, this is easily the most time consuming part of my mixes. The time spent manually adjusting vocals. I can spend a whole day bringing up words here and there, turning down the chorus lyrics since I'm usually belting, and back and forth for hours. Once you have it as close as you can get it by hand, use some compression for the coloring and slight evening out. Don't rely on the compression for volume consistency though.
I take it back. Sorting out and choosing takes is the longest part. I'll usually do the entire song 12-14 times in a row, picking the best words (literally words, not just phrases or lines) and making it fit together cohesively.