You can actually buy Louvre tickets in advance online, and save yourself the hassle of waiting in line to buy them. This is far more convenient. If you buy them online, you’ll need to wait around 10 days for them to be mailed to you (unless you pay extra for rush delivery). I think buying Louvre tickets online is the best option for avoiding long lines.
If for some reason you can’t buy them online in advance, there are a few tricks for avoiding the long queues. If you enter the museum from the Rue de Rivoli entrance, take the escalator down and look for ticket machines. You can buy your Louvre tickets here and there is usually not a wait. You can also try going in through the Metro near the main Pyramid.
In any case, if you arrive early (before they open at 9), you can often beat the long lines at the main entrances.
