Update system

sudo apt-get update && sudo apt-get upgrade

Remove unnecessary apps

sudo apt-get remove --purge aisleriot gnome-mahjongg deja-dup deja-dup-backend-gvfs totem totem-common totem-mozilla totem-plugins activity-log-manager activity-log-manager-control-center brasero brasero-cdrkit brasero-common  landscape-client-ui-install unity-control-center unity-control-center-signon empathy empathy-common thunderbird thunderbird-gnome-support onboard onboard-data gnome-orca unity-webapps-common shotwell rhythmbox evolution-data-server evolution-data-server-online-accounts gnome-calendar gucharmap cheese vino gnome-mines gnome-sudoku xdiagnose usb-creator-gtk remmina* remmina-common* remmina-plugin-rdp* remmina-plugin-vnc*

sudo apt-get remove $(dpkg --get-selections | cut -f1 | grep -P "^unity-(lens|scope)-" | grep -vP "unity-(lens|scope)-(home|applications|files)" | tr "\n" " ")

sudo apt-get autoremove

Execute sudo without Password

Open terminal and execute command

sudo visudo

Add the below line at the bottom

username ALL=(ALL) NOPASSWD: ALL

Replace username with the username of your system. Now press Ctrl + X then Ctrl + Y and then press Enter.

Display full list of startup applications and processes

sudo sed -i 's/NoDisplay=true/NoDisplay=false/g' /etc/xdg/autostart/*.desktop

Now you can open Startup Applications and remove unnecessary applications that starts as ubuntu starts.

Enable passwordless ssh

Add noatime to fstab

disable last accessed time.