When setting your PATH make sure you add to the appropriate place in your path list....as the PATH list will be searched from start to finish to find the command you are after - so adding to your PATH may need to be at the end of at the beginning - depending if you want this directory to be searched first or last.

export PATH=/usr/bin/new_directory:$PATH (will add to start of path list)

export PATH=$PATH:/usr/bin/new_directory(will add to end of path list)

Very important if you have a command or fucntion that is stored within two places on your system - and you want to specify which one to use.