Oh dear, Nebbles, had I known you needed such help. Here we go.
a. how do i tell when someone is flirting
b. how do i flirt
c. how do i not look stupid when flirting
d. how do i pick up signs if he's interested in me
An answer isn't cut and dry, but for the most part:
a) Body language and speech patterns. Are they speaking in ways considered atypical from their normal? Are they more complimentary? Less? Could what they are saying have other intentions(see b)? Do they keep eye contact when talking to you? Do they try to get close to you(in a non-creepy way)? Do they shy away? Pay attention for light perspiration and flushed complexion.
b) Answer me this: what is the objective of flirting? To display/imply/make known your intentions either subtly or not. If the goal is sex, innuendo and physical contact are ideal options as Maestro said. If the goal is a steady relationship or if you are unsure of yourself, compliments and cuteness(batting eyelashes, light giggling) can go a long way.
c)Wrong question to ask. 'How do I not embarrass myself while flirting?' is a better one. Know your comfort zone. If you think you would be uncomfortable doing something, then find something similar that you are comfortable with. Be yourself, I know that phase has been beaten to death, but it's true and more often than not, it works.
d)See answer to a. If they appear to reciprocate your actions/compliments/etc., they are most likely interested. If you are confident enough and think you're both ready, you can just ask.
Flirting is weird. It's all about taking chances, trying to find out what works, like a strange game of mao. As I said before, be yourself, you'll be fine.
