Being social is a thing. Especially for you who claim yourself as introvert. An introvert wont easily change into an extrovert. So I think this text is still relevant as long as we live.
Naturally people like to be liked. And the wisest advice would say: you, at first, should like yourself. Your way to appreciate yourself is shown on how you address people around you.
In certain culture, there are people who seems like they would never ever ever greet you. That is not because of their dislike (hardly), but more likely because of (a) your own shyness, (b) their own shyness, (c) you don't know each other it would be creepy, and (d) unimaginable situation. But there is a fact that you should keep in mind: everyone is lonely. Ex group mate, ex class mate, even people who rarely talk to you during your previous encounter naturally likes to be greeted.
It really wont hurt that bad when they ignore your greetings. Probably they (a) don't hear you, (b) simply don't remember you and that's expected (come on!), (c) are drown in serious thought, or (d) in a hurry. What you have to do just use your courage.
As molsem we are also taught to spread salaam. Not only to people we know but also them who we face on the street. The situation in urban area probably makes greeting to stranger a bit strange, but have you ever randomly greeted in the street with smile and nice words? Simply a greeting, without nosy question or following conversation and of course without any effort to rob you. That kind of greeting could really make your day.
I know that beyond school you should have already mastered at least this greeting part of 'socializing' course. The fact is: not few adults in my circles struggle with this problem. No worries. Let's try fellas!
PS. I think I should post this to my junior high school students as well.