Step 1: Download & Install DiskMaker X

Just download DiskMaker X 3 and install it to your Applications folder. Also, make sure you already have the Install OS X Mavericks file there, too, and a properly formatted USB drive before continuing.

Step 2: Run Through the Easy Instructions

Now open up DiskMaker X and choose Mavericks (10.9). It will find the installer file in your Applications folder. Select Use this copy, choose the USB thumb drive option (if that's what you're using), select the partition you want to erase (e.g. Untitled), and hit Erase then create the disk.

Then, enter your admin password and wait. Once it's done, you should see a notice saying your OS X boot disk is ready.

           

Using Your New Bootable USB Drive

To use your bootable Mavericks USB drive, simply plug in the drive to your Mac of choice and restart (or turn on) the computer while holding down the Option (Alt) key on your keyboard.

When the gray screen comes up, select "Install OS X Mavericks."
From there, you can choose to upgrade your current OS to Mavericks, or you can perform a clean install by erasing your main hard drive in Disk Utility, and then choosing "Install a new copy of OS X" instead.