Read them in this order,# 3 (if you mean the book THE ZONE), #1, #4. Read #2 any time, it's a quick explanation, like handbook. Keep in mind the carbohydrate block lists in these earlier books are somewhat outdated, so if you choose to use the block method, defer to the lists on this site.
That said, the best Zone books to read first are TOXIC FAT and THE ANTI-INFLAMMATION ZONE. They are Dr. Sears' newest books and give the most up to date info. OF those two, I’d suggest reading TOXIC FAT first. They're excellent books for new Zoners and long time Zoners. TOXIC FAT also includes a 28 day starter menu to ease you into the Zone.