Be fit, not just skinny. Fit and healthy is the best thing.
Also people forget about eyebrows but theyre actually so important; they frame your face and can make or break your look. I get mine waxed every few months for the shape (which is quite inexpensive and not very painful) and then tweeze to maintain. If your brows are quite sparse, filling them in can do wonders.
Dont forget about your smile; brush and floss regularly and whiten if you need to. your smile is your greatest accessory, and yellowy teeth and/or a mouth full of cavities isn't attractive, so take good care of that smile and show it off as much as possible, because happy people are attractive people.
You can wear nice clothes, but make sure they suit your body type and skin tone.
Don't overdo the makeup and do not rely on it. Too much makeup, too dark of makeup, or makeup applied improperly is not attractive so make sure you're applying products properly and not overdoing it. Also if you can't leave the house without it, that is a bad thing and means you are reliant on it. you need to have the confidence to leave the house bare faced, people can sense insecurity so you may want to work on that more than anything else.
Last note: you are your worst critic. You may not find yourself attractive, but that doesn't mean that you arent. Have your own back and find a way to accept yourself! Best of luck girl!
If you were not born "hot", work out as much as possible. Hit the gym 5 times a week and do everything you can to have a fit body because most guys have an auto-5 attraction scale wherein, if a girl has a nice body, she's automatically a 5/10. Then leave it to your natural beauty / personality to get you the rest.
1) Be thin but don't starve yourself, you want the fit and in shape look, not the unhealthy look.
2) Dress well
3) make up does help but don't overdo it
4) I can't stress this enough. This will probably help the most. Have confidence. I thought this was just a myth, but no. It works MIRACLES. There's this ugly girl I know, and I mean UGLY. I've noticed she doesn't give a fuck and she smiles with literally the most confident smile I've ever seen on someone's face. You can still tell she's ugly, but it's like you have to remind yourself... Otherwise you forget and you see her as if she was as beautiful as she thinks she is.
Keep your weight off. Limit makeup to eyes and lip gloss. Hair long as you can stand. Non-seductive clothes. Sports bra that lets you bob and subtly shows nipples. I will be calling. You do not have to be gorgeous. "Earthy" is good