Here are a few steps if you want to create a bootable USB stick:

1. open Disk Utility and erase the USB drive with the partition tab
2. choose "1 partition" and "free space" as file system
3. open the Terminal
4. find your USB stick device:

   # diskutil list

5. and type

   # sudo dd if=/path/to/fiile.iso of=/dev/rdiskX bs=1m

Please make sure that you use the correct output device (of=/dev/rdiskX). if you choose the wrong one you could overwrite your internal disk!