Your best bet is to make something that is wanted that other sellers aren't making. My sister's makes quite a bit at some shows selling potholders and similar items. However, the sales at these shows have been horrible for the last 2 years. My sister, who makes doll clothes (American Girl, Barbie, etc.) has abandoned most craft shows now and sells at 'boutique' shows because those who show up to these are not pinching pennies. They buy. The folks who run the boutique shows only have ONE seller of doll clothes and ONE seller of quilts, etc, and they are usually higher quality.
I plan to make sports oriented remote control holders to see if they will sell. My BIL loves his.