Versailles

Head to the Saint-Michel Notre Dame RER entrance.
Take RER-C to Versailles-Chateau Rive-Gauche sometimes labeled as Versailles-Chateau R.G.. This is the stop you want, there are two RER stops in the Versailles area. It takes about 30 - 35 min. to get there.
Head out of the train station, take a Left on Avenue du General de Gaulle to the signal.
Take a Right and cross the street onto Avenue de Sceuax. You can walk down the center along the trees and benches.

This will take you to the Palace, I'm assuming that is where you want to go.

Side note: About the 3rd street on your Left while walking down Ave. de Sceuax is Rue de Satory, half way down on the Left side of the street is a bakery, Artisan Patissier, great place to stop and get some fresh pastries, juice or coffee, to enjoy the rest of the walk to the Palace.

The line for ticket purchase will be to the far left when looking at the main gold gates to the compound.
The line to enter the Palace and security lines up just to the left of the main gold gates, there is usually the metal tubing barricades forming a box and or a security guard nearby.

I recommend getting in line at least 30 - 45 min. before they open, pass through security (if you already have your tickets or the Museum Pass) follow the signs to the Hall of Mirrors. Get all your photos of the room empty of people, then head back towards the entrance and begin your tour. I did this back in Oct, there was only myself another lady that followed me and the two security guards in the entire Hall of Mirrors. Got great pictures, within 90 minutes of my return, it was full of people.

Also, it can take up to 30 min. to walk to Marie Antoinette's Hamlet. You can take the passenger train, rent a bike or rent a golf cart. The Hamlet does not open until Noon. If you get there around 30 min. before they open you can be one of the first ones in. Once you go through security head out the building and follow the path at about 1 O'Clock, this will take you to the main structures and lake. I did this as well and got pictures of the entire area with no one else in them. With 30 or so minutes, it was full of people.

Thank you so much for this valuable information. I will put it to good use.