Winning arguments, is not my ultimate goal, but I would like to be able to defend my life’s philosophy.
Define it! Live it! then, go on to “defend” it.
Given that you say you are “a complete beginner, …[in]… philosophy…”, do not be in a hurry to defend any viewpoint. Indeed, do not be in a hurry to define it to yourself. Just keep asking “why?” on a range of topics, without taking too much for granted. When you reach what seems to be a basic premise, then question that too. Also, on anything about which you conclude: “that’s good because…” also ask “is it also bad in some way?”, and vice versa. Also, on anything that you conclude is good or bad, ask if it is good and bad in all contexts; if not, the ask yourself “why not”?
The problem is that you could do this on your own for years and never get much done. So, the best way is to stand on the shoulders of those who went before. Just as we do not try to figure out the whole of Physics from scratch, it is equally unproductive to attempt to figure out all of Philosophy for oneself. Truth is that you aren’t starting from scratch. If you’re a typical person, you already have been taught some type of philosophy all your life. Most of the explicit teaching would have been in the area of Ethics: you would have been taught about what is good and evil. So, that would be a good place to begin questioning your premises.
At this stage, do not use discussions to defend yourself or to spread your philosophy; use them to learn. So, for instance, if you read one book by Ayn Rand, do not join a Christian forum and argue logically about how wrong they all are. After a single book, you would probably come off as ignorant. You won’t convince anyone anyway, and you will not learn – because you are not listening. At worst, you may come away thinking: they’re all fools, the world is irrational, life is futile.
A better approach for someone at your stage would be focus on your own learning. So, if you join a Christian forum and see a thread of interest, you might approach it like this: ask specific people how they arrived at specific conclusions. The same thing with friends.