Now that you have your negatives safely stored and indexed, you need to sort out which negatives you are going to print. Trying to judge this by holding them up to the light or by laying them on a light box can be difficult. The best way is to produce a contact print showing all the frames on one sheet of photographic paper.
There are special frames that allow you to do this. You can buy contact print frames which consist of a glass top with film holders attached and a solid base with foam on that clips shut. For 35mm or 6x6 (medium format) which hold seven rows of six for 35mm or four row of three for medium format negatives. The frame holds the negatives so you can see the frame numbers on the print, you place them with the shine side up and put a soft grade light-sensitive paper on the base. Then shut the frame to bring the negatives in contact with the photographic paper, hence contact print.
Another method of contact printing is if you use clear plastic negative holders, you can place these directly onto the photographic paper. The problem with this method is it does not hold the negative completely flat to the paper which means that some of the pictures may be distorted. A way round it is a clean sheet of glass that is big enough to place over the negatives.