There's so much to see that you really need a plan of your priorities. The obvious attractions are well signposted. We saw the Mona Lisa then just enjoyed wandering the various galleries.
The Louvre, itself, is a beautiful building inside and out and we really had a great time exploring.
We went for late night opening on a Friday which worked very well. We hadn't pre-booked as I had read that ticketing was fairly quiet on a Friday evening and it was. We purchased our tickets, picked up a map and set off. We were there for four hours and didn't see nearly all of it but were delighted with what we did.
Photos taken with Sony DSC-HX50B.