First disable starting steam at user login by unchecking the box in Steam > Settings > Interface > Run Steam when my computer starts
You need a shortcut to Steam on your desktop.
Right click the shortcut and go to Properties.
Append the text in the target box with
Target box should now look like this:
"C:\Program Files (x86)\Steam\Steam.exe" -nochatui -nofriendsui
Start Steam with this shortcut from now on.
On Linux you can achieve the same results by appending the same options (
-nochatui -nofriendsui ) to the Exec line in the file: