Placement of Adjective
Is this the only correct way, "C'est une jolie fille"? Isn't the adjective after the noun equally correct?: C'est une fille jolie.
BAGS (or BANGS -- N for "newness") is an okay guideline for adjectives, but there are some notable exceptions (e.g. âgé = old, but it pretty much always follows the noun). There are certain adjectives that come before the noun, and "joli" is one of them. This site has a pretty good list. https://languagecenter.cla.umn.edu/lc/FrenchSite1022/ADJPLAbefore.html There are also some possible nuances where you could place the adjective either before or after, but in general adjectives follow the noun, with a few exceptions.
Adjectives that deal with Beauty, Age, Goodness/Badness, and Size (BAGS) come before the noun.
not an easy one, because if you can say 'une jolie fille' and 'une fille jolie', the contrary is not true : you won't say 'une moche fille' but definitely 'une fille moche'. it's by listening how native people talk that little by little you'll remember how to do it.