Hi Steiner, I've been 7 times since childhood. I'll go through everything you need to know.
1. Tickets- the general entrance ticket will give you access to the areas detailed in this map:
https://mapsengine.google.com/map/viewer?mid=zQbIsxJGLQcY.kP4YaI9BXO2M
As well as access to the open pitlane on Fridays.
The pitlane walk ticket tends to be quite expensive and frankly it doesn't offer you much more than what you are likely to experience on an open Friday. As far as grandstand tickets; they are certainly worth the expense especially if it's your first time. Seeing the start and finish in the comfort of a seat and with a great view is priceless.
Sommer and Lagache are good grandstands. The ACO grandstand is only available to members. T34 tends to be cheapest and for good reason. Although it provides for a interesting view of the start/finish straight and is directly above the pits, it bears the brunt of the sun during the day, not recommended if you burn easily. On hot, sunny Le Mans weekends you tend to see that grandstand quite empty during daylight hours. Panorama and Raccordement provide for great views, but again are very exposed to the elements.
If you decide to camp, then the problems mentioned above don't really pose an issue. You can always go back to your campsite for some shade etc. If you aren't camping but commuting to the track, and you plan to stay at the track for the full 24 hours, then having a grandstand seat is great for catching up on some sleep (with ear plugs of course!).
Your seat is reserved during the race, but once night falls, security becomes very lax, you can move around the grandstands and sit where you want. You can do this during the day too, once the race has started and people start to drift around.. Having a grandstand seat also provides for relatively easy access to the customary track invasion at the end of the race.
I would recommend a grandstand seat for first-timers.
2. Camping/Commuting - Having done both, each has its merits. Price and inconvenience are two negatives against commuting, but it also depends on where you're commuting from. If you're based in Paris for example, you have to factor in the TGV train to Le Mans, expense, timing etc. If you're staying in Le Mans, it's less of an issue as Le Mans city centre is only a 20 minute tram ride away from the circuit.
Camping obviously has its upsides and drawbacks, the sense of community versus the inconveniences of camping (especially during wet Le Mans weekends). But camping at Le Mans is one of the things you just have to do.
3. Transport - If you're commuting, there is easy access to the centre of Le Mans via the tram. The tram route also includes the train station which is a 25 minute journey. Buses too are reliable. If you're driving to Le Mans, be prepared for long queues of traffic and hours of waiting. The TGV train from Paris to Le Mans takes about two hours for the standard service or one hour for the high speed service. You're looking at around 150 for the high speed train, half that for the standard train. Take into account French toll roads if driving to Le Mans. This site is handy:
http://www.viamichelin.com/
4. Food - Pricey, but not extortionate at the circuit. But with the city centre so close, have your meals there. There's also a supermarket nearby the race track (Carrefour), so you can stock up on essentials there. There are plenty of bars and restaurants in the vicinity of the circuit.
5. Le Mans Village - Basically a funfair within the circuit, with the big wheel as the main attraction. The big wheel is a must at night, breathtaking views of the circuit are guaranteed. Costs about 5. There's also a range of stalls in the village area, with team merchandise, and some unique sellers. You can spend hours there just browsing, without spending anything.
6. Helicopter rides - Offered at the circuit. Costs 70-90. Seems to be getting more expensive as the years go on. Do not book this with a third party supplier of Le Mans tickets, they tend to charge double. It tends to be a 10 minute trip, with undoubtedly the best views of the circuit, especially at night. If you're on a budget skip it.
7. Facilities - Main toilets in the village. Portaloos in the camp sites. Frankly horrifying, but necessary. There's a lot of alcohol consumed by thousands of people during the weekend, so you can imagine. Even worse when the weather's bad. This is where it pays to be an ACO member. They have good shower facilities and toilets near their grandstand.
8. Exploring - An absolute must. Walking around the track and seeing the cars from different vantage points in something special. Whether it be sunrises at the Dunlop curve or sunsets at Tertre Rouge. Arnage and Indianapolis at night to see glowing brake discs or Mulsanne. You can easily walk to Dunlop, Tertre Rouge and the Porsche curves, but Arnage/Indianapolis and Mulsanne are bit of a hike. But they have a shuttle bus service that runs at the circuit to take you there. It tends to get very busy though at certain times. Traveling the circuit via bicycle is fantastic and a bicycle is something you should certainly consider bringing with you if you're camping. Away from the circuit, you have a lovely city, with a beautiful old town area and a very decent cathedral. The populace are friendly and welcoming. Do explore.
9. Mad Friday - You'll hear plenty about this. Essentially, people congress in certain areas and go wild. Flash cars doing donuts, people with water guns spraying cars going past with water (and sometimes other things), copious amounts of alcohol consumed. Best avoided as it's becoming ever increasingly obnoxious.
10. Drivers' parade - Customary parade through Le Mans city centre. A great chance to see the drivers, but more importantly, the greatest collection of exotic cars you're ever likely to see in one place. Definitely a must-do for a first-timer. Find a place to sit down with a cold beer, then sit back and relax.
That about sums it up, if you have any more questions feel free to ask. My recommendation to a first-timer; camping, with grandstand seats.