A lot of it, from what I have found, goes with spelling it how it sounds. Southern accents are pretty simple since Southern Dialects have a speech all their own. G's get dropped, s's get added, few things actually have a single syllable, O's get changed to U's. Granted that is depending on if you are going Ga Southern, Lousianna Southern, Texas, or Virginian - since they are all their own monsters. 

	TWD Rp I am Gming, for example, has a Virginian, 2 from Boston, 2 from South Ga, 1 from Texas, and a Russian. Each of them speak in their own way, with their own inflection. The Rper who controls one of the ones from Boston doesn't use R's when he speaks. The Russian, v's and w's get interchanged and Th's at the beginning of words then to come out as D's. 

	Though going beyond that, a lot of it has to with turn of phrase. Each area has little lingo's all their own - get to know the catch phrases and it becomes a bit easier. Your traditionally thought Southern Redneck seems to be the easiest for many I have seen to pick up on portray, then branching out. Though, if you live in a particular area, draw on your own experience and try typing how you and others sound around you. 

	I will say though, take it little by little - Been there with the Scots accent thing Broken was speaking about. Lines of text I had no idea what they were talking about. Granted if you are playing a Scots meeting a Redneck and you want them both to be confused as hell by what the other is saying.... Go all in LOL