Things I wish I'd learned sooner:
1) machine needles have fronts and backs. Get 'em in backwards, and you get skipped stitches or none at all.
2) cheap thread is poor economy. ditto cheap fabric. Good fabric and thread at a good price is entirely acceptable, though, says she who just scored 10 yards of Pendleton Black Watch plaid wool at $2/yd...
3) Zippers go in SO much better if you increase the seam allowance in the zipper area to a fat 3/4" inch or 7/8". And zippers go in so much better if you do them like the pros do instead of how the zipper package says.
4) Make sure your patterns are balanced.
5) Always walk a sleeve pattern to see if it will actually fit the armscye or if someone drafted it after being awake for 72 hours. The "awake 72 hours" patterns make wonderful wastebasket liner.
6) If you have to ease anything (e.g., sleeve into armscye), put the bigger side next to the feed dogs. Yes, I know you think you want to check the easing as it goes under the presser foot, but try it my way anyhow. Bet you'll be surprised.
7) A whole lot of sewing problems are actually inaccurately cut pattern problems. Pay scrupulous attention to grainlines and cut the fabric on paper to help stabilize it for accurate cutting.
8) Commercial sewing patterns don't use enough interfacing in most cases, and it's often placed in the wrong spots (like having it stop at a hemline, instead of crossing the hemline, so it can do some good!).
9) Interfacing sold X yards in a plastic bag for a "special price" is generally junk.
10) You can't judge a fusible interfacing by how it feels on the bolt. You have to fuse it and then decide if it'll work or not.
11) Just like fabric, interfacing has grain (well, a few odd sorts don't, but most do!) You need to match the grain of the interfacing to the grain of the fabric... lengthwise grain to lengthwise grain.
12) Some of my best and cheapest sewing lessons have involved a well made but ugly or worn out garment from a ragbag or thrift store. Get out the seam ripper and take it apart, trying to figure out in what order things were sewn. Note type of interfacing used, and where and how it was applied. Digital cameras make it easy to document the project for later reference.
13) Sometimes it's the sewing machine that's screwing up.
14) Most of the time, it's the sewing machine operator screwing up.
15) If you're stuck, chances are there's a sewing buddy available out there someplace on the internet... even at 2 am!
Kay