Measure the space your area rug will occupy. Consider the factors that may affect your measurements. Allow for doors that need to open and furniture, such as dining chairs, that may move within or next to the area of your rug. Size up foot traffic to do what you can to prevent tripping.
Use brown craft paper or tape flattened paper grocery bags together to make a sheet the size of your rug. Transfer your measurements to the paper to make a pattern. This gives you a preliminary look at your area rug--and a final chance to change its dimensions.
Roll up your pattern and take it with you to the carpet store. Especially if your area rug is an unusual shape, laying the pattern on remnants will ensure that you have enough carpet. Having the pattern may also help you in final decisions about carpet patterns--the width of stripes, size of dots, or intensity of patterns.
Lay your remnant on an undamageable surface, face down. Because your carpet knife has a curved blade, sharp to the end, do not plan to cut out your area rug on an unprotected wood, linoleum, or carpeted floor. If you have any doubts about damaging your floor, place a flattened cardboard carton under your carpet remnant--a quick, homemade cutting board.
Secure your pattern to the back side of your remnant with masking tape.
On a part of your remnant that lies outside the pattern, practice using your carpet knife. It can be hard on your hands, and practicing will help you decide if you need help with cutting.
Cut around pattern with knife.
Clean up and dispose of leftovers, except for your cutting board, and try out your area rug in its location.
Make any final corrections to cutting.
Place area rug facedown on your cutting board. Coat edge of area rug with white glue, making a border at least 1/2 inch wide, all the way around and coating all the backing fibers or foam. This will prevent the edge of your rug from raveling.
Let rug dry, glue-side up, for 24 hours. Check to make sure the entire edge of the rug is covered with glue; repair any gaps in glue and let repairs dry.
Lay your rug, throw away your cardboard carton, and enjoy the new look of your room.