Use folders or labels to organise and manage your email. If you have a good reference system set up, you won’t ever have troubles looking for mail. Paper documents are filed for ease of use, and email should be treated the same way.
Keep your correspondence; you never know when you will need it. Most modern email systems provide plenty of space, so it’s good to get into the practice of saving any mail that isn’t junk. That way you can’t be accused of not sending somebody something when you have actually sent it and vice versa. During my career I have referred back to old emails on many occasions and have resolved a few disputes by looking in my archived mail.
All modern email and webmail clients allow you to create rules or filters. Basically a rule or filter is an automatic action performed by your email client as it receives mail. An example of this would be a rule that instantly places all mail from firstname.lastname@example.org into a folder called ‘Receipts for Service We Use’. This way you don’t have to have payment receipts cluttering your inbox, yet you still have easy access to them. There are many uses for rules/filters. I suggest doing a quick online search for more information, tutorials and examples.
Sometimes we find ourselves on useless mailing lists. If you are on a list that is useless or no longer relevant to you, take a second or two to unsubscribe. Just because you once sent some flowers or bought an airline ticket, it doesn’t mean you want your inbox filled with their daily specials.