It's through trial and error and many dollars spent. When I was very fuzzy about aging and knowing how they develop this is what I used to do:
1. I usually buy at least a couple of boxes of something I like.
2. I smoke one cigar from the box.
3. Write a tasting note.
4. Store them boxes. My humidor is constantly at low 60's, temp and humidity.
5. After a few months, Repeat steps 2 to 4.
I however can't do that anymore. Too much work and too much boxes to try. It is however a fun and enlightening activity.