Automation is what you can do afterwards. When recording, don't look at the knobs, look at the level meters.
Keep the track level at 0dB (as the tracks level setting has nothing to do with recording level), and set the soundcard
input level so, that the maximum levels in the track meter are around -6 dB (assuming you record in recommended 24 bit, a little hotter if 16 bit). That way the recordings are at least roughly at the same level. Usually automation is needed anyway, it's very much a standard procedure before starting the actual mixing process.
Recording vocals the other key thing is microphone technique.