Now that I have tell you whata fashion madmoiselle is, I want to give you my advice in nails.
REMEMBER: I'm almost thirteen, and I'm really crazy with some nails, so just remember that some are really crazy looks.
I think that the thing that you should remember is to use, if you don't know how to join the nails with your outfit. The "Francesita" like in Argentina we say, joins everything and it is very classy.
This is the Francesita, look:

Remember that the white line should be thin.
You can make a lot of designs. Now, some celebrities in Argentina wear the line green and the other part black. That is cool, I think, for going out at night to a club. But if you go out with your nails like that in the day, think it carefully, haha.
The other thing that you can do is put stickers in the nail:

Please don't put a regular sticker to the nail. Remember they all should be nail special, because if not the plastic can ruin your nails. And, everytime you put a nail special one, when you take it off, maybe you can water the nails with hot water ( but not really hot) to take out any little plastic. You may have some trouble if you leave the sticker for a lot of time, because it would be harder to take it off.
I reccomend leaving one or two stickers, because if not it may be tiring and bored, to have the same in all the nail. And it may look a little taggy.
OK, that all for now, remember to buy some soft pink or transparent nail polish, they are really cool. And fit with everything.
XOXOXO,
Moré