He wants to see her again. He calls her fairly soon after meeting. He wants to spend time with her in person over phone, Facebook or text. Why? Because he wants to see Ms. Hotness in the flesh.
He is energetic and/or engaged around her. He tries to show her a good time.
He doesn’t give up if he doesn’t score on the first night or on dates afterward. Note: a girl has to decide for herself what commitment she requires, if any, for physical relations.
He brings his best Game, whether it’s PUA style, or some other variation. He isn’t a drag, annoying, a complainer, nor does he have a big chip on his shoulder.
He wants to see her on a regular basis. There isn’t a huge gap between dates – even if he’s out of town, he calls and checks in on her. Note: if he’s dating other girls (which is likely), another girl may be his #1 interest. If a girl is a decent competitor, he will still stay actively interested in the other one; that girl may end up taking over the #1 spot. If a girl is a weak competitor, his interest will be weak too. She should proceed with caution and follow his lead – don’t take things too seriously quite yet.
His interest increases, rather than decreases, over time. He wants to see her more and more — daytime, nighttime, almost anytime.