I found my diary from highschool when I was packing and I thought you all might like to know some outfit/appearance guidelines I made up for myself before I started high school, and followed until I graduated. Hell, I still follow most of these.

For tops:

If the top shows cleavage, no bra.
If the top is sleeveless with thin straps, no bra.
If the top is thin enough to see through, wear either a skin tone bra or a bra that's very visible through the fabric. Lingerie bra if I can.
If the top is white but not thin enough to be seen through on its own, no bra.
When possible, top must be short enough to show the waist of my panties if they're visible and as much of my belly as I can get away with.

Exceptions: Sports bra for gym, support bra if the top is loose, clear straps if I can. If it's cold, use bandaids instead of a bra to cover nipples for tops I wouldn't wear bras with, otherwise just deal with hard nips being seen.

For skirts and dresses:

Rules for tops go for the top half of dresses if possible.
Knee length or longer, no panties OR g string or crotchless only.
Between fingertip and knee length, cover with large bandaid if we have any available (I event through a lot of these at the time. Now I don't bother.) If not, white or skin tone panties, thong, g string etc.
Above fingertip length, if I can get away with it, wear noticeable panties in bright colors, bikini bottoms, or lingerie that isn't g string or crotchless. Thong or cameltoe is best.

Exceptions: Cheap panties during period, panties with more cover during cold weather only if I can't handle the cold. If I wear pantyhose, must be crotchless.

Pants, shorts, etc.:

Thicker pants like jeans, wear bright, high waisted panties. Thongs, lingerie are best.
Thin, tight pants like yoga pants, no panties at all, no exceptions.
Shorts, same rules as pants, except: no panties with loose shorts like gym/basketball shorts, wear either g string or nothing with short/booty shorts.
With low rise pants/shorts, if the waistband of my panties isn't visible, my butt cleavage and the top of my pubic area should be.
Wear tights/hose as pants with same rules as yoga pants, go for as much see through as I can get away with.

Exceptions: Same as for skirts except for the rule about crotchless hose. Thicker pants only during period.

Swimsuits:

One piece, pull tight, light colors only.
Two piece, tied bikinis only, tied in bows (because they were easy to undo, you just needed to pull and they came loose.)
Wear thong bikini if I can get away with it.
Cameltoe preferable.
Always insert a ball, no exceptions (I had ping pong balls I liked to play with. I sometimes put them in with other outfits but I required myself to wear them with swimwear. Later on I sometimes opted for a vibrating egg instead.)

Misc and accessories:

If my toes will be seen my toenails must be polished.
Wax everything (I did it so often I don't even grow body hair most places anymore. I never told mom, she wouldn't have let me, she didn't even want me to shave.)
If I'm wearing heels, as high as I can get away with.
Necklace with cleavage, must be long enough to reach my cleavage.

They weren't meant to be a complete set of rules for every situation or anything but I wrote it up because I wanted to be sexy in highschool and I thought the easiest way to do it was to have rules rules like this. So if I, for instance, decided to wear granny panties with a long skirt for no reason I'd feel like I was breaking a rule and I'd mentally kick myself for it.

I actually added a few things later once I found out that these things existed and I was able to get them (through an older friend.)

I added:

Wear nipple clamp chain under heavy top.
Wear nipple and clit clamp chain under loose/flowing dresses when I can.
Insert vibrating egg when I use a large bandaid to cover myself.
Insert jewel butt plug with longer skirts.
Insert plain rubber butt plug with one piece swimsuits and when wearing regular jeans, not skinny jeans.

Some of the rules I stopped following after I graduated (although I wore nothing under my graduation gown except the nipple and clit clamp chain and jeweled butt plug,) but a lot of them I still follow. I don't wear panties under longer dresses or skirts at all, even if they're slit up the side, I don't wear them under yoga pants or when I wear tights/hose as pants, I keep the waistband of my panties visible over thicker pants, and I follow the guidelines for tops still. I don't use the ping pong balls anymore but I sometimes do go swimming with toys inside me, and I still opt for tied bikinis because there's a chance the string will come undone.

And honestly I thought highschool was pretty fun. I got in trouble a few times and some of the other students called me a slut (which, not really wrong so I didn't care,) but overall I wouldn't change anything. If anything I'd try to go even further if I could do it all again.