You only have to edit your profile file like this:
sudo su
vim ~/.profile
and put this at the end of the file:
export ANDROID_HOME=/home/(user name)/Android/Sdk
export PATH=$PATH:/tools
export PATH=$PATH:/platform-tools
Save and close the file and do:
cd ~
source .profile
now if you do:
echo $ANDROID_HOME
it should show you something like this:
/home/(user name)/Android/Sdk