Do not be fooled by movies and TV, flirting is not always easy. There are so many factors that need to be in line in order for a flirting attempt to be successful. Firstly, they have to know you're flirting. Secondly, they have to want you to flirt with them. Thirdly, you have to sum up some serious finesse.
Maybe it sounds easy when written out in three steps, but it's definitely not something that comes naturally to everyone. That's why it is so impressive when someone actually accomplishes a clever flirting attempt. It's definitely a roller-coaster, you have to shoot your shot, but also read the room. Either way, be careful, It's a crazy world out there.