Decorative topstitching is a great way to add emphasis to a part of your garment and gives it a quality finish. Topstitching is sometimes confused with edge stitching. Edge stitching is one kind of topstitching, always about 1/8" to 1/4" from the seam line, but topstitching is any sewing done on top of the garment. Topstitching is traditionally done on hems and necklines (also 1/8" to 1/4" from the seam line), but you can add it anywhere next to a seam or edge. Try it on jacket lapels, pockets or on a center back seam.
Here are some tips to make your topstitching even better:
You only need a straight stitch for topstitching, but if you have a sewing machine with lots of fancy stitch options that never get used, try those, too. Some sewing machines can create patterns of flowers or animals; these are darling details to add to the pockets or cuffs of a children's outfit. If you are using a straight stitch, you'll want to adjust your stitch length to be a bit longer than you would normally use.
Topstitching is done in a contrasting color thread (because it's meant to be seen), so the stitching needs to be particularly straight; otherwise it will be really noticeable! Sew slowly for precise results. It's helpful to mark a stitching guide directly on your fabric, particularly if you are using your standard presser foot. Using a water erasable pen to mark your lines is a good idea; don't forget to test it first on scrap fabric in case it doesn't actually erase.
You can use regular thread for topstitching, but for the boldest look, use specialty topstitching thread. There are numerous options, including silk thread. Topstitching thread is a bit thicker than regular thread, so you might find it necessary to use a stronger needle with a larger eye. And if you do use topstitching thread, make sure you keep your bobbin wound with regular-weight thread.
A twin-needle (two needles side-by-side) is a good choice if you want topstitching on either side of a seam, like the center back of a jacket. Just be sure to check your sewing machine's manual for threading instructions.
Your standard presser foot is all you need for topstitching, but you can also use a 1/4" presser foot (sometimes called a patchwork foot). The 1/4" presser foot helps a lot in maintaining the distance between the edge of the garment and your stitches, but isn't necessary. However, if you find yourself topstitching on most of your garments, it's probably worth the investment.
Always test your sewing machine settings before topstitching your garment. Sew on scraps that mimic the actual garment; topstitching, particularly when you are using specialty thread, behaves differently on one thickness of fabric than two.
Of course, always press your seams before topstitching. Give them a good press with steam after you topstitch as well, to remove puckering and set the stitches.
Finally, don't backtrack your stitches. This will leave an unsightly mess at the beginning and end of your topstitching. Instead, leave enough of a tail to tie off on the other side.
What garments have you added decorative topstitching to?