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.
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.
Your own voice is your most important piece of equipment. If you're new to the voice-acting world, look around to see if there are classes or coaching in your area. Outside of class, practice speaking clearly and confidently. Learn to do this even with material you've never seen before. It's also important to learn voice care – straining or injuring your voice can hurt you and your career.