Primarily by having multiple email addresses and aliases.

I realized that on many occasions, I'm giving out my email merely as part of signing up for an account or resetting my password. So I made accounts and aliases that I use when I don't forsee a service sending any messages of value after I sign up. I star the confirmation email for my records and ignore whatever junk mail comes my way, first-party or third-party.

As for the main personal email I use to actually communicate with people, my provider's built-in spam filter has done a good enough job so far. If it misses anything, it usually follows a pattern (topic, domain, etc.) so I just make my own filter rule. In the off chance I do want messages in my main inbox from a service after I sign up, I do so with an alias. If that alias gets compromised, I just cut it off.

Granted, I don't see much spam anyway since most of my email is work-related, my employer's IT department seems to do a good job of filtering out spam, and I'm strict about not using my work email outside of work.