Your sewing machine is your friend.
One of the first questions I ask my students is what their sewing experience is. Usually it is somewhere in the range of having-never-sewn-a-thing-before to having-completed-a-few-projects-successfully. Occasionally I even get someone who has never even taken their machine out of the box. Needless to say, most of my students don't have a thorough understanding of what their machines can really do for them.
Usually people just sit down and sew. Occasionally, they might adjust the stitch length or switch from a straight stitch to a zig-zag, depending on the projects they are working on and what the pattern suggests. Don't get me wrong, this will get you pretty far in sewing. A straight stitch and a zig-zag for edge finishing are mostly all you will ever need, but what about all those little levers and dials on your machine? What do all those things do?
First of all I would suggest getting out your manual and looking through it. This is a very useful tool that often goes unused. It might be just the thing to understanding how to make a button hole (I bet it is easier than you think), or using your zipper foot. It also usually describes a variety of other stitches and why you might use them. If you don't have a manual for your machine, try the good 'ol World Wide Web. They are pretty easy to come by online.
After you have your manual in hand and are ready for a little thrill, try this; it is an exercise for all of you who are afraid to touch anything on your machine for fear that you will forever wreck it and never be able to return it to the original factory settings:
1. Sit down at your machine with a couple pieces of solid color fabric in a neutral. An old scrap of a woven cotton shirt will do, or a fresh bit of muslin, nothing with stretch, just simple cotton is preferred. Two layers is best.
2. Take a deep breath. It is only a machine and you are going to take it out for a little play time.
3. Put in some thread. Doesn't matter much if it is cotton or poly, just make sure it is in a contrasting color to your scrap of fabric.
4. Sew. That is right, sew. Play. Start with a straight stitch, what ever you have your machine set on is a good place. Use a pen, any old one, and write on the fabric where you have your length and width set. Maybe a length of 2.5 and a width of 0. That is about the usual for a straight stitch.
5. Here comes the fun part. Change the dials! Flip the levers! Push the buttons! With each change, flip, or push, sew a new line of stitching, and note on the fabric scrap what you did. Maybe the length is now all the way to 5 and the width is still 0.
6. Keep going. Try all your decorative stitches. Try zig-zags at different lengths and widths. Try overcasting stitches (see your manual), and blind hem stitches (see your manual). Keep making notes on your fabric along the way.
7. Have fun with this. You are making a handy little reference tool that you can keep near your machine. You can pin it up on the wall or tuck it in your tool bag. Next time you are ready to sew something you can take a look and find the perfect stitch for the job.
Sometimes your projects will improve by making subtle adjustments, like lengthening your stitch for topstitching, which allows the stitches to show a bit more. For finishing edges, try making the zig-zag stitch a little wider than usual.
I like to change things around on my machine and have 100s of decorative stitches. There are little diagrams that show how each stitch should look, but they do the stitches no justice at all. Having a little swatch of fabric that really shows me what they are is so much more helpful.
I had the opportunity to do some of this sort of thing in a class when I purchased my machine. Many people purchase machines that don't come with classes or receive them as gifts or hand-me-downs. This fun little activity will really get you out of your straight stitch comfort zone and help your sewing confidence grow.