If you have never been before you'll love it, but get there early. Buy your tickets as soon as you can and on race days drive in early, park up and take a picnic with you as it gets a bit manic. A good grandstand is the one on the final corner before the start finish (looking towards the church) as you can see the start straight, then the three final corners as they wind back up the hill (and, quite often, crash into the walls and other cars).
The Bugattis are a sight for sore eyes and interestingly, most of the field comes from the UK generally.
Take a hat and a waterproof jacket (i.e. normal Le Mans attire) - it can get sufferingly hot in the middle of the streets with all the people around too - last year temps got up to 40 odd degrees in the grandstand, but the year before it p*ssed down ....
Don't forget too the Rallye the day before (the route is kept secret until Thursday evening but then published on the website and you can plan a route to lay in wait as they come by and enjoy a picnic by the side of the road, or stop at the lunch stop and drool at the cars parked up). They usually stop for lunch somewhere near Cognac (last year lunch was at the Hennessey factory in Cognac so all the cars were parked up along the banks of the Charente).
Finally, there is the 'Concourse D'elegance' in Angouleme town centre on the Friday and/or Sat evenings.
We are only about 40 mins away but not sure if we are going or not this year. PM me if you want a contact number in case you have any other questions etc.