There are literally hundreds of threads worth of tips and so on here 911CG. Many of us are 'old hands' but we all do Le Mans in different ways. Some even have websites all about their escapades.....
(No, not just me!).
I don't know whether you have grandstand seats (I suspect not as you'd have mentioned it by now I guess), but the whole of the area from before the Ford Chicane right round to Tertre Rouge is easily accessible on foot. Stake a place early on the tribunes opposite the pits on Saturday as that gets crowded very quickly, or even watch the start out at somewhere likeTertre Rouge. As Simon says, if you can, try and get out to Arnage/Indianapolis or Mulsanne Corner during the night...