I have a double light switch in my living-room that I want to cancel out for the time being
Always turn off the power at the service panel before working on any house wiring. 

The particular method depends on how the switches are wired. 

If each switch has three wires (including the ground) connected to it, then the solution is very easy. For each switch: leave the ground wire connected, disconnect the other two wires from the switch terminals, straighten the ends, twist them together, and screw a wire nut onto the ends. 

If any switch has more than three wires (including the ground) connected to it, then you need to make a diagram or photo to get help deciding which wires to twist together.