How do I decide what to sew?
First: Figure out what skill level you have. I mean, most people don't start learning to sew by constructing a white silk-velvet wedding gown. It's possible, but ... seriously? If you need a formal and it's your first go-round, have it made. So - don't pick anything you can't sew.
Second: And that means don't pick anything that you can't fit. If it's a dress that's make-or-break with perfect fit (like a sheath dress), even if the pattern company rates it "easy to sew" - that only means the technical sewing skills, not fitting. Word to the wise.
Third: Figure flattery... this is where it gets fun. But easy-fun. Pretty much every book on style has a "what to wear/not to wear if you have X figure". Use those - preferably the older the better, as they tend to have more specific instructions. Also, drag the stuff out of your closet that looks incredible, and look at the style lines.
For me - I'm not easy to figure-flatter, and that's why I tend to have something of a uniform. I'm 5'2", I'm busty, I have a prominent abdomen, short legs/long torso, square shoulders, and a short neck. There are clothes I simply do not wear, mostly because I don't burn to look like a candy apple.
There are fine details - did you know that the busty among us do not look well in kimono/dropped shoulder seams? We don't. We need the definition. Shawl collars for the square of shoulder? Ugh. So there are any number of fitted vintage patterns that simply go into the "next" pile in my brain. I know that I *must* have a shoulder seam at my shoulder. New books might have this information... or they might not. Check a vintage style guide to get your ideas. (I have a great one by Edith Head that is oh-so-helpful).
Know your sartorial limits. And don't be tempted by the clever fabric, the new lines... or even worse, the styling. I have an entire book of patterns that is virtually unusable, as the person who wrote the pattern book and I share almost no figure points. She looks great - and I like her look. But when I try to pull off the road she took to get there? Oh dear.
Fourth: Colors - I've written about this before, and I'd truly enjoy figuring out what colors look best on anyone who wants to send me a well-lit picture. (If this floods, I might take that back, lol). But wear your colors already! :p Don't cheat.
Fifth: Texture - I find I look best with a bit of texture. Satin and I don't get along. My best friend nearly makes you cry if you see her in chiffon, it suits her so perfectly. Work with this.
Sixth: Fabric content/drape - use the weight of fabric recommended on the pattern unless you're very experienced, in which case, why are you reading this? Fabric content - I'm a natural fibers snob, but truly - if you're going to get it dirty, it had best be washable. If it's going to the office, I guess you can wear polyester. If you want to do that. -shudder- It's cheap and it comes in lots of patterns/colors. But make it work with what you're making. Unless you're ready to break all the rules - day clothes are cotton/linen. Office clothes are silk and wool and shirting fabric. Evening clothes are shiny/special. Use something that makes you happy - but something you'll get some use from.
Hope that helped someone, I got a bug in my ear to write a bit about the style lines, having flipped through a few pages of vintage patterns just now.