He Makes Steady Eye Contact
Eye contact is one of the most obvious ways to flirt with a guy and to tell if a guy is flirting with you.
If a guy consistently holds your gaze from across the room, he is probably looking for a sign that it's OK to come over and talk to you. If you are having a group discussion and a guy constantly looks at you specifically when he talks, it's probably because he's interested. Even on a date, you can tell a guy is really into you when he makes and keeps regular eye contact.
He Asks Questions
When a guy asks you questions about yourself, your life or your preferences, it's usually because he wants to get to know you better.
If you are chatting it up with a guy and he continues to ask you about yourself, that is a very probable sign of flirting. Asking questions not only gives him an opportunity to show you he is interested, it also keeps the conversation going. On the same note, when guys end emails and text messages with a question, it is usually because they are interested and want to keep the conversation going.
He Already Had the Opportunity to Leave
If you are at a party, a bar or even out running errands and you meet a guy who starts possibly flirting with you, analyze whether or not he's had the opportunity to leave.
If his friends have passed by multiple times, his phone rang, his order already appeared and he's still talking to you, he's probably flirting. Most guys don't continue talking to a girl they're not interested in if they have already had an out to end the conversation.
He Indicates He's Single
If a guy asks you openly or indirectly about whether or not you are seeing someone, it's probably because he wants to ask you out.
When you are talking to a guy, if he casually mentions that he just broke up with his girlfriend or any other remark to let you know he's single, it's also probably because he wants to ask you out.