Even if you're mixing yourself, it's better to add EQ and compression only when you can hear how it will sit with the soundtrack or special effects. Ultimately, it comes down to knowing what your voice will be used for and making a judgement. For instance, if I'm recording a tagline for a TV or radio advert, I'll generally run a mic into a nice preamp (where I might add slight tube warmth, and subtle EQ or compression, just to give the recording a bit of 'body'), and I may do a little de‑essing using a plug‑in when performing any edits. However, for e‑learning jobs, corporate videos and so on, I'll tend not to add any creative processing while recording or editing, and will only use the de‑esser ever so slightly.
Also listen for sibilance. Strong 'ess' sounds are best corrected at source, by using good mic technique, but sometimes they're unavoidable. If you hear an 'ess' that really sizzles in your recording, you can manually reduce its volume. You can, of course, also use a de‑esser, but do be careful, as applying some de‑essers to the entire audio file can alter the sound of your recording. It often works best to apply them to short sections, either offline or using automation. My preferred de‑esser plug‑in is the one sold by Eiosis (www.eiosis.com),Make sure you record some silence at the end of each take. That way, if a great performance suffers from noise issues, you have something to feed your noise‑reduction processors. Just don't rely on this technique too much! which cleverly separates the esses from the rest of the audio and allows you to manipulate them independently. If you want to learn about some more advanced strategies for de‑essing check out Mike Senior's article from SOS May 2009 (/sos/may09/articles/deessing.htm).
As editor, you need to turn the raw recording into the final version of the file you'll be sending to your client. Editing during a recording session can be problematic, and particularly so if you're recording in a domestic environment. How can you expect to hear the drone of the dishwasher ruining your recording if the dishwasher is still running as you edit? I'll look in more detail at setting up a voiceover recording studio next time, but for now, if recording in a separate room or isolated booth isn't an option, at least try to edit the file the following morning (or maybe at night) when there's less noise around — because hearing your recording with a fresh ear and in a quieter environment will help you to make better editing decisions, and will reveal noises that slipped your attention earlier.