If your connection box is full and it is difficult to insert the device (switch or receptacle), find out what kind of wire connectors, if any, are used. There is a type called “wing nuts.” If you have this kind, do the following.
After installing the wire connectors on the wires, cut the wings off the wing nut with diagonal cutters or linesmen pliers. Do this as close to the body of the connector as possible. You may be surprised how much easier it is to position the wires inside the box after the wings are cut off. If you have to remove the wing nut later, you can easily do this by grabbing on to the wing nut using linesmen pliers, then twist off.