How can I make Safari cmd+number shortcut switch tabs instead of opening the bookmark associated with that number?
In case you are coming from Chrome and want to use 

cmd+[0-9] for switching tabs (instead of cycling through your preset top sites) take a look at:

github.com/rs/SafariTabSwitching


  Safari Tab Switching is a Safari SIMBL plugin which allow switching between tabs using Cmd+1-9.


Update:

Safari Version 9.0.2 (El Capitan) has native support for this: