Getting to Versailles is quite easy: Just take the RER C train from Paris to the end of the line towards "Versailles Rive Gauche - Chateau de Versailles". That is, if the train line is not on strike as it was when we traveled to Paris last month and on at least one other time. Your hotel concierge or desk attendant will probably be well aware if the line is on strike. BTW, Versailles is closed on Monday.
Go on a Wednesday: We have had people walk away from Versailles after seeing the massive crowds on weekends. Other days are crowded too but we find Wednesdays to be the least crowded. Perhaps it is because many French school children only have half day school on Wednesday and field trips are not planned for that day.
Plan on Crowds: Whoever is managing Versailles has not figured out a way to manage the crowds like is done at the Borghese Gallery in Rome. Be prepared for a LOT of people. You can take the strategy of getting there early in the morning (like everyone else does), but that rarely works. However, it is probably better to arrive late in the afternoon.
Only Go With a Reservation or With the Museum Pass: Even on "light" days lines can be substantial (more than 1 hour) just to buy tickets on site. A reserved time, or better yet, The Paris Museum Pass offers quick entrance. UPDATE: On our last tour to Versailles in April, 2017, the Paris Museum Pass DID NOT offer quicker access. We had to wait on line like everyone else.
Bathrooms are Inadequate: Be prepared to line up for the restrooms. Bathrooms are woefully inadequate to handle the crowds, especially for the ladies.
Bring Lunch: I'm sorry to say this, but food services are shameful. Not only are the facilities inadequate, members of the staff will probably not win personality contests. The system for selecting, purchasing and paying for food is slow and inefficient. Good luck trying to find a place to sit and eat - bonus points to you if you find a clean table. Try eating in the gardens. I question the quality of the food. I inspected a sandwich that was labeled as being made 4 days before the sale date.
Something Always Seems to Be Under Construction and Closed to Visitors: For instance, on our last visit, the Queen's Bedroom was closed and the Hall of Mirrors was partially closed. Didn't they just spend years on renovating the Hall of Mirrors? And why oh why can we never get in to see the amazing Opera at Versailles? I have not seen it in several years in multiple visits to Versailles, including last month. And with the construction going outside of Versailles, it looks more like the Shanty of Versailles instead of the Chateau of Versailles. There are boarded up buildings, construction debris scattered about, scrawled signs with poor and confusing information directing visitors to various entrances.
No Meeting Point: If traveling with several people, it is important to set up a meeting point for your group. The problem is, with the way they have directed pedestrian traffic, it is hard, sometimes impossible, to make your way back to previous parts of the chateau to meet others. Wouldn't it be great if they designated some official meeting points for those who get separated? How about free wireless connections for us foreigners without international cell phone service who want to text others in our travel party? Surprisingly, no one has thought of that either.
I really don't want to be negative on Versailles but a visit could really be a much more positive experience if it were managed better. All you can do as a traveler is know what to expect and prepare for it.