How new is "new"? You talking about pre-Cobra Civil War stuff, too?
edit:
Pre-Civil War (the initial IDW launch), each series can really be read pretty much independently. And I would recommend you read each series straight though when you can..otherwise, some of the plots can seem to drag.
1) Cobra (the best of the three). Starts with a 4 issue limited series. Then a 2nd 4-issue "limited series" (called Cobra II) that got extended and lasted 13 more issues. Most highly recommended.
2) GI Joe (the main series). There is a minor cross-over with GI Joe: Origins (a Mainframe-centric) issue, but other than that, can be read straight through. At the end of the last issue, they reference an event which happens at the end of Corba II's run, so I would make sure you finish the Cobra series first.
3) GI Joe Origins (pretty much hit or miss...some great issues, and some really awful ones). You can get by if you skip this. All these issues occur before the main series time line, so you can read these in any order. As I said before, there's one cross-over issue involving the origins of Mainframe that ties into the main series (and when you get to that part of the main series, they'll tell you.) Otherwise, you can save this for last...a lot of it is filler.
All three end at the same time to launch Cobra Civil War. If/when you pick that up, again the three main series (GI Joe, Cobra, and Snake Eyes) can really be read independently.