Lighting a space in the round adds a dimension to a lighting system that is not present in most theaters. The usual set up is to have almost all the light coming from various angles in the front, with some from the sides. In the round (or rectangle as you may have it), much more light is required in order to fully illuminate the stage and the actors from all sides. This requirement means that although you may think you have lots of lights when you read my list of equipment that follows, you will find yourself strapped to evenly illuminate the stage.
When you are talking with the director to see what needs to be lit, make sure that he/she/it realizes your limitations, you will have enough lights left to have a few specials (lights that are used for special purposes), but you will be unable to have very many. You will also not have the ability to change the color of the light on stage at will, unless you are willing to have one of them very dim.
Anyway back to what this section was supposedly going to be about ... the lighting plot. In short this plan is a drawing of the stage at the level of the bars from which you will be hanging you lights. After talking to the director and finding out what special things they have in mind, you will want to design a layout for the placement of the bars and lights upon those bars.
A very standard setup is to have three bars hanging length-wise (east-west) in the center of the commons over where your stage area is going to be. One or two bars can be placed cross-ways (north-south) in order to fill things in somewhat. At the stage level break the stage into six sextants, and worry about lighting them individually.
Each sextant should be lit by a minimum of four Fresnels, two on each of the bars that surrounds the sextant. This Fresnels should be placed opposing each other so the the actors are lit from four different directions. The Fresnels should be placed so the they are pointing nearly parallel to the bar. You will want to fill in the areas using Par Cans from farther away, but they will be used to flood large areas at once, whereas these Fresnels can all be wired so they end up on the same channel on the lighting control board allowing relatively easy control over the lighting level in an individual area.