I like to print my negatives with a grade 2 or grade 3 filter. I reserve 1 and 4 for emergencies and the exceptions. So for my proof I choose something in the middleŚ2-1/2. With the negative in contact with the printing paper and held tight with glass, I want an exposure that will turn the paper beyond the negative black (when developed), and the clear edges of the negative just matching, viewed in good light (sun). If this takes 10 seconds, a 9 second exposure will show some discrepancy between the film edge and black paper beyond. So, proof to black, or proper proof.
This way, you can judge how your shadows and highlights and overall tone show on your contact sheet, and will let you know if you need to allow for varying film exposure and development in the future. If it looks perfect, great, but this proper proof is instruction for making more negatives.
If the proof looks all flat, or white, or less than inspiring, make a second proof sheet with an adjustment to contrast and exposure, so that the proof pictures look nice and appealing. This way you can see the potential in your negatives, and even though these negatives might not be perfect, you can still (probably) make a great print.
With your proper proof to guide you, your next film will probably be a little closer to perfection, and thus be that much more willing to yield a great print.