A great way to work smarter in Outlook is to use Rules.
Instead of having all of your emails saved in your Inbox for future reference - which can be a unwielding especially if you start getting to lets say 500+ or even 1000+ emails in it. To me this is equivenlant of having a physical filing cabinet with out hanging or manila folders in it and piles of papers are just dumped in it with out organization.
First, setup some folders that relate to the various things in your inbox that you what to save. I setup folders based on Projects that I am working. Do whatever works for you and helps you work the most efficiently. If you want to do it by date or people and that works great.
You can setup up subFolders under the Inbox or under your Personal Folders either one Outlook rules will move items into the folders specified based on the criteria setup.
Some things to keep in mind: Rules setup to move items from the Inbox to the subFolder of the Inbox is a Server side rule and Outlook does have to be running to run for the Rule to work. Note, if you are on an Exchange Server you may have a limit to how large your mailbox can be and these will included in that count/limit.
Rules setup to move to a Personal Folder is a Client side rule and Outlook must be running. If you are moving items from the Mailbox to a Personal Folder then the items will no longer be backed-up by the Exchange Server, if you are indeed on an Exchange server. So just keep in mind about backing up your Personal Folders.
Also keep in mind when setting up rules that there is a steadfast limit of 32KB for all rules combined. You usually have to have numerous rules to reach that limit but just keep it in mind when setting them up.
Work Smart - let Outlook rules do the filing for you.