It's easy to load up your Mac's menu bar with useful add-ons that give you quick access to settings, information, and fast data entry, but it's also easy to quickly fill up and turn into an unmanageable mess. Apple lets you rearrange the items in your menu bar (just Command-click and drag), which is a nice start, but if you need more control over how you see everything you packed in, it's time to turn to third-party apps.
My MacBook Air menu bar is pretty cluttered...
My favorite app for taking control of an unruly menu bar is Bartender from Surtees Studios. It's a quick download, and once installed and running, adds a drop-down menu bar that holds the menu items you want but may not need to see all the time. You set what's in your regular menu bar and what's in Bartender.
...but Bartender makes my menu bar easier to manage
To see the stuff you packed away into Bartender just click its menu bar icon, and you can set items that change their state -- like Tweetbot's icon changing color when you receive new messages -- to briefly appear in your menu bar so you don't have to continually check for changes.
Bartender is a must have app on my MacBook Air thanks to its limited screen space, and it helps cut down on distractions on bigger displays, too. It's US$15 and available for download at the Mac Bartender website, and you can try it out for free for a month, too.