Question: things to do after installing debian 9 stretch?
Answer: Setup SUDO and install Synaptic. These two programs will ease the process of installing programs and performing the administrative task. ... 
Install Whisker menu. ... 
Configure non-free repositories. ... 
Install Key Applications and Packages. ... 
Configure drivers. ... 
Configure firewall. ... 
Speed up the boot time. ... 
Configure lightDM.