I have been writing PHP code for a few years already. When I first started out, I am like you, a self-teach
programmer umm, whatever.
I have a goal. I want to write a Pokemon browser-based game. I asked around what languages do I need to learn. Someone on an internet chatroom told me, HTML, CSS, JavaScript and most importantly PHP.
With that set in mind, I went ahead to W3Schools and learn HTML. It took me a week or so (can't really remember) to learn this markup language (not programming!). Then I know that CSS is a styling language and I don't really want to do front-end work, so I skipped. I get onto JavaScript and learnt that this scripting language is client-based and my RPG game do not need it, I skipped it.
Now that I am at PHP level (congrats!), I gone through a few chapters and stuck at .. I think loops. And then I stopped for a few months because loops is hard. One day I come back and think that maybe I should just skip the loops part, my RPG don't really need it. So I develop my own PHP based RPG game using on simple PHP statement and IF/ELSE and SQL code that I copy and pasted.
Published my game on the web. Guess what? It is hackable with XSS and SQL injection! Some kind person told me about it. With that, I shutdown the game and continue to learn PHPWell, I wanted to write a short story of mine but it is getting longer and longer. If you didn't read it, it is okay, because I don't proof-read it too.
Anyway, what I have learn so far as a self-taught web developer.
1. Never give up - I stopped and learnt PHP twice before I get it.
2. Have a goal - develop something you have interest in.
3. Always go the extra miles - don't stop because you think you're done. Think of something new to add onto it.
4. Start building your portfolio early - you are still under 18, you have plenty of time to build a nice looking portfolio.
5. Learn to say no - don't take on too many projects. Take one at a time.
Three or four years ago, I was still a newbie without any PHP experience. Today, I am a good PHP application developer. I've developed a few MyBB plugins and Joomla modules. To add on, I also have my own websites that I made from scratch which is getting more and more users everyday.
I just started my own Bitcoin & Crypto forums with custom plugins with my friend, look at my signature if you are interested.
(Oh! And have an idea of what type of developer do you want to be. If you want to do games, go with C++ or C#. If you want to make web application, go with PHP. Go is another language that is getting more and more popular and you may wish to check it out.

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