I have been a professional PHP developer for almost four years now.
One thing to really remember is you will never, ever stop learning. Every day you will pick up something new, but that is just part of what makes it enjoyable. Even if it is messing around with HTML5 and CSS3, or just some functions in PHP you've never had to use before.
In your working environment you obviously cannot be as cavalier as you are in your home one. One thing many programmers fail to realise is a business case to do something is very important. It might be well and good fixing that ten year old code that just looks horrible, but unless there is a real reason to, normally it's broken is one that works. And not just 'broken'. I mean, actually broken.
Don't be too quick to pick up on the 'next biggest thing'. There are plenty of narcissitic know it alls in programming who are quick to point out how amazing they are because they are using Virtualisation/Memcached/etc. Technologies, certainly have their place. At the same time, think about the scope of your projects. A common fault of many a programmer is overengineering a solution.
Don't be arrogant, but be confident but modest. Judge everyone on merit, not just years of experience or education. One of the best programmers I know has no degree, or I believe A-Levels. A willingless to learn, and flexibility will help out massively. I've seen plenty of people describe themselves as seniors, or even middleweights who couldn't tell you the difference between require and include in PHP, or knew anything about SQL injection. I would say I was a middleweight today, but never was ashamed to be a junior.
Another really useful trait to have is the ability to talk to people. At at previous company a developer would actually send back stack traces to a manager to explain why something wasn't working, but being able to describe things in simple terms is golden. It's actually useful to be able to jump between a few levels of technobabble actually. Of course, sometimes you might need to explain simply how something works.
If you can, have a home project to work on areas you would like to learn. You don't have to do it all the time, but it can help keep some enjoyment when you are going through more boring patches.
On a PHP front, and I am sure I will be lambasted by some for saying this, but avoid too many Frameworks whilst learning. You tend to learn 'their' way of coding, and their classes and you tend to lose a bit of experience in doing things for yourself, and if you aren't careful you do get a bit lazy, as is evident by some of the other code I have seen recently.
Do not ever be afraid to ask questions.