No one flirt the same way, but there are often similarities. From what I observe in other girls and in myself, the main similarity is how much she smiles. If she is constantly smiling or laughing, she is most likely flirting with you. For one, flirting is fun and it makes people happy, so it's no wonder she is all smiles. Another thing is that she wants to show you that she finds you interesting by showing that she is happy around you. This can be a bit hard to tell if the girl often smiles anyway, but usually her smiles will be brighter or something like that when she is flirting. I know that when I'm flirting, I can't help but smile all the time and laugh at the things he says even though they're not even all that funny.
Another way is to see how she talks. If she is talking slower or faster than she normally talks, that shows that she is nervous. She could also show that she is nervous by fidgeting with a lot of things like her hands, playing with her hair, fixing her clothes, or something like that. Nervousness is usually a good sign because she is most likely trying to flirt and impress you in some way. When I flirt with someone who I really really like, I know that I will play with the straps of my bag or with my cell phone. If those things aren't within my reach, then I'd start rubbing my hands together and straightening out my clothes. But if I'm just flirting for the heck of it, I would be more confident and tease him instead.
Lastly, if she tries initiating physical contact, then she is most likely trying to flirt with you. But keep in mind that if she doesn't initiate physical contact, it doesn't automatically mean she isn't into you. Some girls like touching while others don't. So those who are comfortable with touching will probably touch you when they're flirting and those who don't like touching won't. But if a girl who doesn't like touching touches you, then she is definitely flirting with you. I'm a girl who hates touching and being touched by most people, so I only touch people I'm attracted to and flirting with (unless they're my parents, my sister, or my best friends).
Just remember that not all girls are the same. These are just a few common signs, but that doesn't mean every girl will do all of these things when they are flirting. Like some girls are very confident at flirting and won't appear nervous. There are also some girls who just likes touching EVERYONE, even people who they aren't trying to flirt with. Anyway, I wish you luck!