Question: first things to do after installing ubuntu 18.04?
Answer: Check for Recent Updates. ... 
Install All Missing / Additional Drivers. ... 
Install GNOME Tweak Tool. ... 
Enable and Start Firewall(ufw) to Enhance Security. ... 
Install some useful tools. ... 
Install FileZilla and Screenshot Tool(Shutter) ... 
Install full multimedia support. ... 
Install your Favorite Browser(Chrome)