The first thing I require most in my darkroom is to make a set of dodging tools and set the blades for their prints. The gridded paper idea is what I also use. I have each take the paper, measure about 1/2 inch from the edges and draw a sharpie type line. The grid is drawn with thin ink lines, in about 1 inch squares. Next that paper is placed in the easel and pushed tight to the left side. Now they can place their negative and see the paper, without the blades in place. I have them focus and center the image. The outline shows them consistent margins, if they are working with 35mm they must print the full frame, and so they move the guides to the edge of the image. I then have them outline that margin with a colored ink. They then do their 120 image and their 4X5. that gives them a guide for each type they may print. they repeat the process for 11X14, and 16X20 ( printing frame only can give up to a good 16X20). Many of these easels are older and the blades do not like to be moved, so I tell them, set up for a number of prints and try to plan your printing. They have nice even white boarders. For prints that will be cropped, the crop is made by the blades and the print still maintains the the ratio of an uncropped print.
For really large like the 20X24's or the 30X40's I print, I have made a type of frame with heavy mattboard that is effective. It is modeled on the saunders we have, I will glad to explain it to anyone that is interested. yours Michel