I suggest you look around this community forum, videos, resources. Also look at IVC which is the website internetvoicecoach.com. They have a lot of basic information there for free. Tons of people are always asking this question, so for the veterans sometimes they get tired of assisting people new to VO, but others are sometimes very willing.
I wanted to answer as best I can about sustaining your breath. Don't! Breathe! Try to do a few sentences at a time if it is a longer narration, but generally try to speak normally. The only trick I use is to take breaths in between sentences so they can be edited out later. Pause a tiny moment before and after the breath, and then it's really easy to edit out / remove it later. Also, another trick is to breathe so softly that you can use a 'noise gate' to eliminate it - but that only works to a degree. And timing might be wrong if you have slow quiet breaths, so you just have to practice and see what will work for you. Reading the script in advance to prepare is also helpful for planning the best places to breathe.
thanks a lot, you said you are not sure whether you might be of help, but really you are, all i need is tips and how you do yours.
i figured out all you said just today, and coincidentally, you said the same thing, i know you are god's sent. thank you once again