Versailles is one of the most popular visitor attractions in and around Paris, so here are some tips that may be useful for your visit.

The Chateau de Versailles is generally open Tuesdays through Sundays and on French holidays. So make sure to plan ahead, lest you end up arriving on a Monday and missing the main feature of the town of Versailles. The park and gardens are open every day. You might also plan ahead so that you see the Grandes Eaux Musicales, a spectacular display of waterworks that is unrivaled, although the loud piped chamber music may not be to everybody's taste.  Be aware that the fountains are only activated between 11am and 12pm and between 3.30pm and 5.00pm.  So if you take the official advice to arrive early and spend the morning in the chateau, you will need to wait until mid-afternoon to see the fountains. A day in Versailles is enough for a quick visit, but an extra day allows time to fully appreciate its grandeur.

You can easily get to Versailles by train. You can take the RER C5-Line in the direction of Versailles-Rive-Gauche.  The Chateau is a short walk from the train station, and though it may not be obvious where to go once you get off, it’s always easy to follow everyone else.  You can buy your ticket at the metro station to include zone 5 which is where Versailles is located to save you buying a separate metro & rail ticket. Check in advance for engineering works: they may not be indicated very clearly in the RER station - an alternative route is to take the SNCF train to Versailles Chantiers from Montparnasse, although it's a bit of a hike from this station:

On busy days such as weekends or public holidays prepare to queue about three hours to visit the chateau, 45 minutes for just the gardens, and at least 45 minutes for any ladies toilet facility. An organised guided tour will help you queue-jump the chateau, but you will still need to wait in line.

Beating the queues: when you arrive in Versailles you may see people handing out flyers about tours and pointing you in the direction of a tour office.  For once actually take them up on their advice and it is worth buying the "all-access" pass to Versailles (€25 in advance by internet or €27 at the tour office as of May 2011). This way you avoid the queues at the ticket booth at Versailles itself (but to get in visitors still had to stand in line for 35 minutes with tickets in hand - it would've been much longer without tickets).  They offer packages including guided tours or with access to the King's garden. But if you want the ticket that includes the palace and Marie Antoinette's hamlet, buy the "all-access" pass.

Once at the Palace you'll have to queue to get your bag scanned before entering. When you get inside you can pick up an audio guide (included in the "all-access" pass). Then it's pretty easy to follow the crowds around the main palace. There is also an interesting post-revolution art exhibition on the upper floor.  Give yourself a couple of hours to view the main palace.

Then if you'd like to visit Marie Antoinette's hamlet this is about a 20-25 minute walk, making the mini-train a popular option. Do keep in mind that there is an additional charge for this (€6.70 for round trip in May 2011) and it does get popular so you'll most likely have to queue. It also finishes before the attractions close so be careful to note the time of the last train as otherwise you'll have to make the long walk back yourself.

Food: there are cafeterias scattered about but they are a little pricey, so why not pick up some food in the town before you enter and have your own picnic in the gardens.  Note that food is not allowed in the castle.  You have to check it or chuck it.

If you have any energy left it is nice to walk around the town of Versailles itself. There are some nice squares located near the market area where it's possible to eat out.

All in all, this is a full day's excursion so it's worth setting aside the whole day to visit so that you have time to explore fully.