It's dead easy DJ - even I can do it
The most difficult thing is getting clients. The rest are just technical problems.
Start off with a reseller package from a reliable host. You can pay as little as £10 a month for a fair amount of bandwidth and disk space.
You then need to decide on your pricing structure. Most people decide on several packages of varying bandwidth, disk space and features. The trick is to oversell your resources, because most customers will not use their full allotment of bandwidth and disk space, you can afford to sell to more people than you have resources to support. Make sure that the Host you are buying your reseller package from can quickly upgrade your reseller package should one of your customers take you over your bandwidth and disk space limits.
If you are just selling hosting to people you design web sites for it is even easier - you are completely in charge of the web site settings.
Hope this helps