Many years ago I was taught by gallery directors and framers how to wire artwork...these are the rules I still follow today. My tools include a measuring tape, marker, awl, single or double hole D-rings + screws, mid-weight picture hanging wire and cordless screwdriver with two bits - star and square (use depends on the screws that come with the D-rings). Most of these items are available in hardware or craft stores and I have even found some at Walmart.
The first thing I do is measure the height of the piece and divide that number by three as the hardware should be attached 1/3 of the way down the back of the artwork in order to hang properly. Using my marker, I place a small mark at that point.
Whenever I attach hardware to larger pieces (ie. 5 feet or larger) I use the double hole D-rings and attach them vertically without using any wire. This way the piece always hangs straight and doesn't tilt every time a door is closed.
Fortunately, because I work on stretched canvas, the painting doesn't typically weigh too much so I can usually use smaller D-rings. At this point, I hold the ring in place while I use my awl to place an indent onto the wooden stretcher bar through the hole on the D-ring.
The awl indent makes placing the screw easier as sometimes the kiln dried stretcher bars can be a little tough so I occasionally need both hands to apply pressure to the screw head.
I typically pull the hanging wire up through the bottom (near the canvas) of the D-ring so there is a tail of at least 4-5 inches (depending on the size of canvas).
In order to keep the wire from slipping loose, I wrap the wire around and pull it through a second time. I pull the wire fairly taught but leave a little room for give so that the piece is easier to hang onto a hook on the wall. If I'm wiring a number of pieces of the same size, I will hook my measuring tape onto the wire and measure to the top of the painting just to be sure the pieces will be easier to hang when exhibited.
Wrap the wire tightly so that the possibility of stretching is minimized. Some people wrap tape around the wire and though I don't I do sometimes use a crimper to tighten the wire.
And finally, I label the top (back) of every piece with the title, date, and my name. This same method of wiring is applied even if the piece is framed, just utilizing the exterior measurements of the frame instead of the actual artwork. If there are any questions, please let me know and I will try to answer them as best I can. I hope this helps.