Well you can start with all the FAQs here on this forum. I'll link them for you below.

Then one of the most commonly recommended books on the subject is Seed to Seed by Susan Ashworth. Another is The Complete Guide to Saving Seeds by Robert Gough.

Dave

Here is a link that might be useful: Seed saving FAQs

And the second thing I would do -- check some info as to how long seed can be kept. I suggest doing a goggle seach outside GW.

One website listed three different tables of years for the various veggies -- and they were not all the same.

I sometimes save seeds longer than the suggested years on the package, so maybe only 30% germinate instead of 75%.

Awaytogarden. web site -- if I spelled it right

This site gives seed life info from four sources.

For spinach -- they all are different! From 1 to 5 years.