Reddit user enthros discovered a very effective and simple way to destroy unwanted advertisements in your inbox: filter on the word "unsubscribe". This is because pretty much every newsletter and advertisement is required to have some sort of text that provides instructions on how to unsubscribe.
The problem with this method is that you will catch some dolphins with your tuna (which is to say you'll filter out some things you don't want to filter). To avoid this, you'll need to whitelist certain addresses in your filter so they're not immediately trashed. There may be a few mishaps along the way, but if you're plagued by email ads it's probably worth the trouble.
Alternatively, you could also just automatically move the filtered emails out of your inbox so you don't see them. Once you have a filter that's functioning as desired, you can start sending it all to the trash. Pretty neat! For more tips and tricks, check out our guide on eliminating spam email from your inbox.
Note: Gmail users, if you don't yet know how to create a filter read these instructions.
Best kept secret in email [Reddit]