The first thing you do, contrary to common belief, is be around him or her a lot. Without looking or acting like a creep (so don’t hang around his or her apartment complex!), find out where your target spends time and be there too; a coffee place, a library, a beach, a golf-club, whatever place it is, find a way to be there too. Make sure they notice you and start being friendly only as a friend (nothing more, so do not even think of showing your feelings to him or her at this stage). It has been proven that, unless the initial reaction is very negative (or the initial meeting is associated to a very negative experience), repeated exposure to the same person (in a positive, friendly manner) makes us like that person more and more. So, repeat your contact in a positive way over and over, as a friend, as a great person with lots of things to do who happens to be there or sharing the same interests (or the same friends).
And, just when you know he/she is truly beginning to like you (more than just as a friend), you apply the law of scarcity, namely you become, suddenly and inexplicably, less available. The human mind attaches value to things which are not commonly available, such as diamonds for example, and they take for granted things which are commonly available (even if those things are truly much more essential to us, such as the oxygen we breathe). This does not mean that you leave the love of your life in the lurch or in a tough spot without helping them; it just means that you simply are not there all the time when they expect you to be. The secret is not to have them take you for granted in the long run and, in the short-term, to have them wonder about you, if you have a new boyfriend or girlfriend, why you are suddenly not available, and so on. As their mind is creating scenarios they will build a large desire to see you again, consciously or subconsciously.