GOPATH should be set to a newly created empty directory. This is the go "workspace", where it downloads packages, et cetera. I use ~/.go.
For example:
mkdir ~/.go
echo "GOPATH=$HOME/.go" >> ~/.bashrc
echo "export GOPATH" >> ~/.bashrc
echo "PATH=\$PATH:\$GOPATH/bin # Add GOPATH/bin to PATH for scripting" >> ~/.bashrc
source ~/.bashrc
