This is a piece of advice I recently gave a friend of mine who is just straddling puberty, with all the attached insecurities and apprehension. Only after our conversation and after checking with a few friends did I realise what a true information bonanza this is. Know this about women and you know all you need:

What counts most, and foremost, with a woman is effort.

That's it. It doesn't matter if you've no idea what you're doing, if you're scared or uncertain. As long as you're not bored, crude or oblivious, you're in with a chance.