Know the Craft
The first and foremost thing to do is to be able to do it yourself. Master the craft or at least be proficient in it and understand the technical aspects of the business so that once you start, it is not something that you have to learn by trial and error and you are aware of the technicalities.
Study the Market
Study the market for work and see what different types of options are available. The business has been growing well over the last few decades and with the arrival of internet, your market is certainly not limited to only local companies anymore and you can very easily approach a global market. Do keep in mind which segments of the market you feel more comfortable with and are inclined to working in.
Look for Artists
Voice-over business is about having talented artists who can deliver well. You will need to find a few in order to get a company started. They should be selected after thorough testing and make sure that they have versatile abilities so that they can do more than one kind of voice-over.
Set up an Office
You will need to set up an office which also has a studio with all the required facilities. If these are new and latest in nature, that will be a help as the clients will feel confident that you can provide them with the best work.
Contact Potential Clients
While you look for opportunities that have been posted through various media for voice-over work, you can always get in touch with companies that need such work even if they have not advertised any jobs. This will at least let them know that you are in the market and may give you a small job just to try your service out.