I felt like this would be a worthwhile article considering the high number of improperly wired electrical outlets that I have encountered over the years.
If you look at the back of most receptacles you will notice some small holes in them on the back. Usually there will be 4 holes back there, two on each side. These holes are designed to push the stripped wire into the back of the outlet.
Bad design and bad practice. Don't use these holes for the outlet electrical connections. Always turn the breaker off to the circuit that you are working on.
If you look on the sides of the receptacles you will see 2 screw in lugs on each side. If you don't see any of these lugs on the sides of the receptacles then do not use these receptacles. Now, one side will have silver screws and the other side will have brass colored screws. Always remember white to silver and black to brass.
The white wires in your house wiring are the neutrals and should tie to the silver screws. The black wires are the hot wires and should go under the brass colored lugs. Some outlets will have 2 whites and 2 blacks and some may have just one each. The green or bare ground wire will tie to the green screw on the receptacle.
The proper way to do this is to strip back the insulation from the wires about 3/4 inch. You should now have 3/4 inch of bare copper wire showing. Take your pliers and bend a curl in the bare part that you just stripped back. This curl will slip right under the side lugs on the outlet and tighten the lugs down with a screwdriver. Some wire strippers have holes in them to insert the wire and bend the perfect curl.
After you have the wires connected to the outlets just carefully push the wires back into the boxes and push the receptacles straight back into the box also and tighten the 2 screws into the 2 holes in the box. Below are some pictures showing the proper way and the improper way to wire the outlets along with a pic of the stripper hole to bend the curl in the wire. 
The above picture shows the proper way that receptacles should be wired.
The picture below shows an improperly wired receptacle. I have ran many trouble calls due to receptacles wired this way.
This picture below shows the holes in a pair of Ideal strippers that you use to make the perfect curl in the wire to slide it under the side lug on the receptacle and tighten down for a nice tight trouble free connection.
Where you can run into double trouble with the quick wired receptacles is when aluminum wire is used. The instances are rare but they do exist mainly in older house trailers. If you are aware of anyone that may have this situation with aluminum wire and quick wired receptacles, I strongly advise having a qualified electrician repair this situation asap to avoid problems and a possible fire hazard.
