Luckily for me, I already had a few canvases that someone gave me so I didn't have to spend money on them. For you, try a thrift store or a craft store and buy some with coupons. You'll still be saving a lot of money.
Once you have your canvas, measure the dimensions. Make sure you buy enough fabric to cover the entire canvas and be able to staple it in the back.
As you can see, it doesn't have to be perfect. However, if you are going to place the canvas on a table like below, when you fold the corners, fold them on the sides. That way there won't be a slight bump on the bottom when you place it on a table or shelf.
Start at the top, stapling the corners and the middle. Then pull tightly (but not too tight or you might create lines) at the bottom and staple the bottom corners and the middle. Then do the sides (corners and middle). Once you have those staples in, staple the rest, about 2 inches in between staples. Hold the fabric tightly so it's not loose in the front.
Tip: For big canvases, use big prints. For smaller canvases, you can use smaller prints.
If you want to spice things up a bit, take some painters tape and create a chevron pattern on your canvas. Then paint the exposed fabric white and you will have white chevron stripes that create a modern twist on your design.