Where is a good site to learn about what books look for?
What kind of books do you want to collect/sale? Classics?
Your favorite authors?
Or just books for profit?
When you figure this out, the publications page in the book will normally say "First Edition" or "First Printing".
The page that has the books printing company info/copyright, etc.
Look up the first printing titles and publishers on the internet and you will know what markings to look for.
If it doesn't say "First Edition" or First Printing" but has a series of numbers:
1 2 3 4 5 6 7 9 10 or 10 9 8 7 6 5 4 3 2 1
These are 1st Editions. Anything with a 1, either way. If it begins with 2, etc. it's a second, etc. printing.
I always try to get books with the dust cover or original binding. Make sure the binding is intact and there are no dog-eared, torn pages. Another tip about the binding, know the difference. Look up book binding to see what I mean.
If you are collecting for profit, research which books are selling for high profit either on book selling sites or eBay and look for those books.
GL!