I'm on about my fifth "career".
Actually, let me think about it... I've been a soldier, a tradesman, a nerdier-than-thou IT weenie, (in that IT period I was an engineer, a project manager, a business owner and a technical writer) and now I have kind of an odd strategic thinking job that suddenly went from being IT related to now I do my strategic thinking about very blue collar logistics. I have truly had to learn an entirely new skill set every couple of years for the last 20.
Here's my honest advice: it's life, just roll with it. Pick something and do it. There will be things about it you like and things about it that you don't. When you get an opportunity to do something that sounds like it might be interesting, take it! Stretch the boundaries of what you're comfortable with and don't settle.
It seems like the big plans we make rarely work out, but little decisions have far reaching consequences that we can only see in the rear view mirror long after the fact. For example... Because I decided to take a job in the trades back in 99, my wife now runs a company that does the same thing that I was done doing by late 01. I've known her since she was 19 years old, and I assure you, that was not her plan. But she loves it! Honestly loves it and the people she works with.
Life is going to throw a whole lot of things in front of you that will stress you out and you will have zero control over. Don't amplify it by trying to decide now what you're going to be doing in ten years because you'll likely be off that course in three. There are some guiding principals in my life that I try to adhere to that have served me well...
Know yourself and seek self improvement
Your job, no matter what you do, is to make your boss look good. If you have a good boss, (s)he will take care of you for doing this. If you have a bad/abusive boss... Move on.
You can't control what anyone does, you can only control how you react to it.
Stand up for yourself, but pick your fights carefully. Know when you can't win.
"I screwed up, it won't happen again" is always better than a bs excuse
Teach others what you've learned
Never ask anyone to anything that you won't do yourself
Be nice, to everyone, as often as possible. Being a dick is a tool that you use when it's necessary. Over use diminishes effectiveness.
The world is full of douchenozzles. If you find yourself trapped with someone who is completely unreasonable, move on.
Say good morning to all your co workers every day.
Buy lunch or a drink for someone on your team once in awhile. Being good is important, but you can be the best, and if you're unliked, you won't go anywhere. I've learned this lesson the hard way more than once.
Find a mentor
If you ever get really comfortable with what you're doing, it's time to move on. Stagnation is the first step on the road to mediocrity. Life is a journey, why the hell would you want to pull over on the shoulder and wait to die?
Dress well
Be someone that can be depended on, but don't let yourself be abused
Eat the elephant one bite at a time
Wow, that's a lot of typing before coffee. Sorry about the dump, I guess I'm feeling a little philosophical this morning.