Measure the dimensions of your suitcase or bag.
Look at the various items that you intend to pack in that case and where you want to position them in it. Measure the largest items if you intend to make lots of small compartments on one level so you make big enough dividers.
Cut pieces of cardboard out in the shape of the dimensions of the base of the bag/suitcase so that they will fit correctly. Alternatively, cut out smaller dividers which can go on their sides to divide the area up into compartments on one level.
Pack your bag with the layers of luggage separated by dividers with the one you need to access the quickest on the top. Alternatively, pack all your luggage on one level and place dividers as compartment walls so that your luggage does not get mixed up and is easily accessible.