Previous Step: Making the Corset
First of all, an Elizabethan corset was not meant to diminish the waist. Its goal was to flatten the chest, and to provide a nice, smooth, cylindrical torso. If you pull it really tight in order to make your waist smaller, You'll end up with a waist two inches smaller than it was beforehand, a lot of discomfort, and an aching back by the end of the evening. It's the point of your bodice, and the size of the bumroll that gives the illusion of a small waist.
Elizabethan corsets, when worn correctly, are not only bearable but actually comfortable. For large-breasted women, they provide more support than any underwire can dream of. They also provide terrific back support. First of all, put on your chemise, or whatever underdress you're going to wear under the corset. Wearing a corset against the skin gets it all oily and sweaty and gucky, no matter how machine-washeable it is. Next, find someone to help. It is possible to put on a corset by yourself, which I'll cover at the end of the section, but help is always great.
The corset can be laced up from the top to the bottom, or from the bottom to the top. Wherever you end is where the most pressure will be on the corset; if you're worried about the corset slipping down your waist, lace from the top to the bottom. If you're worried about your bosom slipping down, lace from the bottom to the top.
In period, only one lace was used for the corset. It was tied around one grommet hole, laced across, laced up diagonally, laced across again, and so on, forming a zigzag pattern. There's no reason not to do this, save that two laces are stronger than one and that the one-lace method sometimes ends up with the two sides of the corset uneven with eachother, if you're not careful. If you're lacing with two laces, simply lace the corset up like you would a shoe. Criss-cross like.
One woman suggested lacing the corset from top to bottom, criss cross, and tying the ends together at the waist and pulling the two loops at the bottom to tighten the corset before tying the loops together in a bow.
Lace the corset loosely, then have the person being laced pull on the ends of the laces while you tighten them. Most people will have to do the "Lift" maneuver when the corset's about halfway laced, to create the notorious Elizabethan cleavage. Tie the ends in a bow (a double bow, if you're insecure) and tuck it inside the corset.
To get into a corset yourself, you'll need a really, really long lace. Lace the corset when you're still out of it, from the top to the bottom, as loosely as you possibly can. Then put it on over your head like you would a shirt, and pull the laces to tighten it. Twist, contort, and jump up and down a lot, and eventually it will be securely laced.