Use kraft paper or newspaper to create a template of the floor you're covering. Be sure to cut around any fixtures in the room. Use masking tape around any curved areas. Also, write directly on the template any directions you think you'll need, such as the location of windows or doors.
Note: If the room you're working on has a threshold, allow for extra linoleum so you can run the seam under the threshold. Make sure the template covers the entire area—you don't want the finished piece to come up short.