Everybody seems to suggest folders; I suggest Categories.
I have 1 active pst and 1 pst per archived year, every mail is assigned one or more categories. Adjust folder view to group by category.
The main advantage is that you can assign several categories to a single mail.
Everything that still needs attention is in the inbox without categories.
Oh yes, and Rules! As already mentioned, rules for automated emails, as well as a rule for known senders, which files incoming mail into a special inbox folder.