Start with varieties meant for pickles as they are important for pickling quality pickles..
A brine is at least 50% vinegar, 50% water, and usually salt.
Use good quality vinegar.
Pickling salt is free of additives that make a cloudy brine. While it is best to have a clear brine, an iodized salt does not pose a risk to safe canning.
Additives for crispness: alum is used as are grape leaves and Pickle Crisp type additives are made of calcium chloride .
Processing times – refer to this link as it is so useful! https://extension.psu.edu/lets-preserve-quick-process-pickles
Pasteurized versus canned, as well as steam canning may give crisper pickles.
Finally, fermentation can give the very best pickle of all so check out our episode about fermentation for more or check out the excellent book Fermenting Vegetables by Kirstin Shockey.