You will notice that wires that go into your breaker box are much longer than needed to get to their connection. This extra wire provides flexibility as to where to attach the wire as well as prevents possible stress on a too tight wire.
When you curve a wire to put it under the screw head of an outlet or switch, does the wire really seat fully under the screw head? Milton Albright of Albright Electrical Contractors in Toronto, Ontario showed me how he manipulates his needle nose pliers to end up with a curve and a hook, that allows him to then grab both sides as in the photo after it is under the screw head and close the loop tight to the screw. Just be sure you don't have a lot of extra wire sticking out that could short circuit on something else near-by.
Remember that all electrical work requires a permit, some provinces allow homeowners to do their own electrical work and some provinces require liscensed electricians to carry out all such work. Click here for information on the LEGALITY OF DIY ELECTRICAL WORK.