You can save yourself time and keystrokes by utilizing the toolbar for actions you perform on a regular basis. There are several different places you can customize the toolbar depending on what action is being taken. Basically, anytime you open a new window within Outlook and see the small drop-down arrow referenced below, you can add or take away items from that toolbar.
You can customize the toolbar in the home view, when composing an email, when reading email, when you have a calendar event open, etc.

Click the small drop-down arrow to see some common toolbar preferences.

After you Click an option, it will show on the toolbar and you will have to repeat this process to add each additional command.

There is another way to add more than one command at a time and to see more available commands. This time after you Click the small drop-down arrow, Click More Commands.

The Outlook Options window opens and takes you directly to the Popular Commands menu. From here, Click the item to highlight it and then Click Add to make it appear in the right-hand column. Double-clicking the option will also make it appear in the right-hand column. Once you’ve made your selections, Click OK.

The options you chose will now show on the toolbar ready to access with a single click of the mouse. Some items that were available to choose from are already within a single click on the ribbon of your home view so there’s no need to clutter up the toolbar with repeated.

You can access even more items from the Outlook Options window if you click the small drop-down arrow and choose All Commands. This opens up a huge amount of options that you can scroll and add to the toolbar.