The bias of the fabric is important. Study which way the fabric “gives.” Pull and stretch on it and remember which way it stretches the most. That’s the bias. Once you understand what the bias is, you can make your own bias tape by cutting fabric into strips. Cut the strips diagonally (with the bias) so that the bias tape stretches and gives. You can also substitute bias tape for facings. That’s kinda easy. Facings can take a lot of extra fabric. If you have a small piece of fabric that you’re anxious to use but it’s short for the pattern you have in mind, you can use bias tape in place of the facings. It won’t have quite the thickness and support as facings but in many cases, it works just fine. You can also save two or three inches of fabric by using bias tape on the bottom of pants, instead of folding the fabric and having a typical hem.
Suellen Ocean is the author of many books on diverse topics. Her books are available here: http://www.amazon.com/Suellen-Ocean/e/B001KC7Z78