As stated, start with a reseller plan.
However, most importantly, don't signup with the first host you find that has "Reseller Hosting" plastered on their site.
Do your research about a host you're interested in. Don't settle for the first name you hear. Many people get burned this way.
Once you have your reseller account in place, start by selling some space, or even providing some small accounts for free to your friends and people you know.
This will help you get your feet wet in the world of supporting your customers.
To answer Artashes' question....
Typically, a reseller will face all of the same technical issues that a datacenter faces. The only difference is, when the reseller has no control over the server, things start to get bad as the issue becomes more advanced.
Typically, a customer will see their host (reseller) as no less than a datacenter themselves. Thus will submit tickets and request support the same as a direct customer of the datacenter. A reseller with no server access however will typically have their hands tied in more advanced situations. They generally will not have anything to do but contact their upstream, who in fact has to contact their upstream at times.
Just remember, to a customer, you're not a "reseller". You are a host, that is hosting their website, business, livelyhood. So when problems occur, you will be the direct line of communication. It is then you responsibility to make sure things get fixed, even when you don't have the ability to do so yourself.