There are a couple of things you need to address.
1. Why are you entering the hosting business?
2. Do you have the expertise and time to look after your clients? Remember these people could be running business's that rely on you!
3. Work out who you want to target (market wise) then do your research not only on the market but also who your competition is.
4. From your research build your business plan
5. Research hosting companies that offer reseller hosting and spend time talking with them, feeling them out, getting to know them. You want to be sure they can support you when you have clients down your neck
6. Develop plans/packages that can sustain your business.
7. Find a good billing system! WHMCS, Modernbill are two that are out there. THIS IS IMPORTANT!
8. Once you're out there hit the forums, spend a little on advertising and always look at ways to get your name out there.
9. Take care of your clients! These guys and girls are the reason you are in business and word of mouth advertising is ALWAYS the best form