Modest clothing covers both nakedness and the thought thereof. Immodest clothing draws attention to what is beneath it and calls nakedness to mind. And let me also say that less the notable exceptions of hard-won weight loss or true anorexia recovery, no one earns her body, and thus it is a very silly thing to show off.
Right up front I'll tell you I haven't kept all these rules. Metanoio. Further analysis below.
--Cleavage, except on busty society matrons at formal events. I'm pretty sure you have to be at least 60 to qualify for this.
--Clothing which appears to have been painted, pasted, or spackled onto the body or a part of the body, no matter how much skin is covered in fabric. It is very possible for a turtleneck, layered tops, or a floor length dress to be immodest, as my beautiful associate notes below.
--Tops cut so low that everybody gets an eyeful when you bend over
--Ill-fitting clothing resulting in gappage and overhang
--Exhibitionist undergarments (vanity or peekaboo straps)
--Clothing through which undergarments are visible
--Midriff exposure (unless you're dressed traditionally in India--yes, culture is also a part of this discussion. But let's stay focused.)
--Skirts or shorts shorter than low to mid-thigh (please note, a skirt's length is measured from the highest point of its slit, not its lowest point on the leg).
--Clothing which makes it obvious that the wearer is wearing a thong or is lacking one of the two standard female undergarments (sorry, hippies).
--Clothing with detailing which draws attention to the places where everyone already pays attention without the helpful direction of seams, sequins, or stripes.
--Clothing with "cute" expressions like "Eye Candy," "You Wish," "Please Mentally Rape Me," etc.
--Unlined skirts or dresses without a slip
--Also, athletic events are not an excuse for cleavage or cling. You can wear a t-shirt. It will not kill you.
Inappropriate for church includes all of the above plus:
--Cleavage, ever. This includes bridal parties. I cannot believe this needs to be spelled out. A bride can still look absolutely beautiful in a wedding dress that shows she belongs to her husband alone rather than everyone. If you must cleave, save it for the reception. And then ask yourself, especially if you're the blushing bride, why must I cleave? Why do I want a whole bunch of people looking at my boobs?
--Clothing requiring specialty underclothing (halter, criss-cross, asymmetrical, or no straps or a low back: all these call attention to what's under your dress, since it obviously isn't standard). This excludes by definition spaghetti straps and strapless or backless tops/dresses. Save all these "cute" items for garden parties.
--Scoop necks, deep Vs, and loose collars of any kind. Kneeling, folks. Think about it.
--Skirts shorter than knee length. Bowing, ditto.
--Heels so high that you can't walk in them without wiggling
--Anything clingy or tight on any part of the body
--Also, dresses or tops with buttons must be checked for gapping. If two-sided tape can't take care of it, retire that piece or buy the next size up.
"Style" is one of the falsest aspirations of humanity. No female has a right to wear any particular article of clothing, even if she looks great in it, even if it's what everybody is wearing, even if it's so cute and she really really likes it. Also, for maternal types, they're not "my clothes" if they don't fit me. Get some that do for early pregnancy, postpartum transition, nursing, and whatever else throws off your measurements--that's what thrift stores are for. My wardrobe is a mile wide in sizes and an inch deep in any given size. Sigh.
Now, I realize that it is very difficult to buy clothes for your exceptionally unique body, for someone your age, etc. Girls, deal with it. There are certain styles which simply cannot be worn modestly on certain body types, and certain styles which are immodest, period. I'm sorry. Your body may also be proportioned such that you have to select certain styles of clothing to modestly fit your largest measurement rather than your smallest one. I'm sorry about that too. I don't like it either. I'm fully aware that it often doesn't look as good as we all want to look, and the misery of having a size that big in your closet.