So simple and I observe myself recently, I notice that I:
a) Try to call her at least 3 times a week
b) Flirt her
c) Keeps on asking or dating her out even she resist
d) He sometimes not behaving like himself like he's trying to catch ur attention with his act
e) He usually will show up at places u frequent, and he will say "Hei, never thought to c u here"
f) He will ask a lot of questions about urself
g) He will act differently when u told him that someone else is going after u
h) He tries to have a same hobby like u even he's not into it. Example, u like guys that can play guitar and can sing, if he really like you he will go to the  extent to learn it to entertain u
i) He tries to call u at somewhere around before u sleep
j) He tries to find out about ur activity with who u usually hang out with
k) He will think a lot and ask u questions like "Ur phone out of credit", "U sleep early is it, thats y u din pick up my call" n make many stupid assumptions
Hope that helps u fren. Anyway this is wat i observe that happen to me recently.anyway that gal oredi rejected me