The quality of your voice over depends almost entirely o the skill of the voice actor you use. A good voice actor will have perfect enunciation (ie, be very easy to understand), speak at an ideal pace (not too fast and not too slow), and have a pleasing voice. They should also be good at acting, and able to convey the feeling or emotions required by the script, using vocal variance and tone to keep the words interesting while also embodying the desired mood.
The advice we present here is tried, tested, and true. Peter Dickson is the foremost leading professional voice actor in the UK known for voicing the X-Factor, Britain’s Got Talent, Live at the Apollo, The London 2012 Olympic Games and countless brand commercials. In a stellar career spanning 40 years, he has worked on over 120 TV shows and series, many of them award winning, been a promo voice on 60 TV and Radio channels around the world, been a featured voice actor on 30 AAA game titles, and voiced in excess of 30,000 radio and TV commercials!
Not all noise can be tackled in this way, though: you need to listen for clicks, plosives, digital glitches and the like. These can normally be acceptably repaired by using a 'heal' tool, or a pencil tool to redraw the waveform. Popped 'p's can often be 'fixed' using a high‑pass filter set at 100Hz. For a single glitch, you can zoom in and cut out the cycle of the waveform in which the glitch appears. Just be careful to start and end the cut where the waveform crosses the centre line, otherwise you'll inadvertently add another digital glitch. If glitches are frequent, it's likely that there's a problem with your audio interface's buffer settings — it may be just a playback issue.
Once you’ve identified a pool of candidates based on skills and availability, look at their experience and browse their gig gallery. Listen to samples of previous voice-over work to get a sense of their style, and choose the candidate whose style you like best. You can contact them before ordering, explain your project requirements, expectations, and budget, and provide examples of work you like by the seller or someone else as an audio reference.