Working with a top voiceover agency can bring you a steady stream of well paid work. The top voiceover agencies, like Hobsons in London or Abrams in NY and LA, have an elite set of voice actors as well as recognised visual actors who do voiceover. These top agencies are hard to get into though. They only take the very best established voice talent.
At this point — unless you're tracking for broadcast applications (where they don't work to peak levels) — consider 'normalising' your recording to an optimal level. Normalisation can be used to push the loudest peak to around ‑1dB and increase the volume of the entire recording by the same ratio. Of course, you can also tighten up dynamic range (the difference between the softest and loudest parts of your recording) by manually reducing the loudest sections of the recording before you apply normalisation. On a final note, if you do plan to use a compressor, then you might as well add gain at that stage instead of normalising.
As the engineer, your key job is to select and set up the recording space, choose and position the microphone, set levels and make sure you're recording a good, clean signal at a healthy level. Like music, the louder the signal you want to record, the less audible the noise floor, but you don't want to have to speak louder than sounds natural, and you don't want to overcook things when tracking: any distortion will be very noticeable on an exposed voice part, and an otherwise great take with digital clipping won't be acceptable. If you notice clipping only when you start editing, software clip restoration tools might help to make the take usable, but it's not going to be perfect. Remember that although you may have needed to record 'hot' on analogue tape and older 16‑bit digital recording systems, modern 24‑bit A‑D converters can accommodate a much wider dynamic range, so you no longer have to track so loud: you can leave much more headroom.
This is the number-one issue most people bring up when they discover they have to do voice over work for their video. Let’s face it. Most of us rarely have to hear our own voices in audio recordings. We’re used to the rich, warm sound of our own voices in our own ears. There’s no way around the fact that you sound different on recording that you do to yourself.
A demo recording of you doing voice-over work is your CV and your business card combined. If you're applying for a voice-over job, you can send the potential customer your demo via the Internet. Ideally you have multiple demos for different types of gigs. For commercials, clients want to hear 60 to 90 seconds of voice work. If you're auditioning as an audiobook reader, five minutes of demo proves that you can stay in character over a longer stretch of time.