What proven ways do you recommend for enhancing your intrinsic motivation at work? How does it work?

I'm assuming that you really did mean "intrinsic motivation", being motivation derived from actual enjoyment of the task at hand, as opposed to from rewards or consequences that might follow.

Now, finding "proven" techniques for "enhancing" motivation is kind of... questionable. It sounds a bit like a tag line for a trashy self-help book sold on TV. So I'll use the closest I know of: Daniel Pink's Drive: The Surprising Truth About What Motivates Us. Other than that, I'll be speaking from my own experiences.

As a full time student and part time wage-slave, I struggle with finding motivation in my work on an hourly basis. I've managed to do so better than many of my peers, and this has been the result of a handful of techniques which I will outline below. You'll notice they follow nicely from Drive, which I would recommend reading. They also relate back to two things: how you approach your work at any given junction, and the ability to choose that approach yourself.

If you haven't read Drive, here is the Twitter summary provided by the author:

Carrots & Sticks are so last Century. Drive says for 21st century work, we need to upgrade to autonomy, mastery and purpose.

Autonomy:

Hopefully your work affords some of this key ingredient. Otherwise, you will seriously want to talk to your employer. If you have a set of tasks, the ability to choose which one to work on is critical if you want to enjoy the undertaking itself. This is pretty simple: if you have a set of tasks you could be working on, and only one you will enjoy working on, work on that one first!

Okay, but what if you only really have one thing you could be working on? Here's the most effective concrete technique I can offer on this topic: if you have a project that you don't think you will enjoy, try to divide it in to subtasks you might. Work on those first, and succeeding in those will hopefully give you enough motivation to carry through on the rest. This works for me all the time.

The connection to approach is obvious. If you have the ability to choose what you are approaching, go with whatever intersects enjoyment earliest.

Mastery:

I like to say "mastery and its pursuit" because I love learning new skills. For me, intrinsic motivation often arises in large part from one of two things:

1. Doing something I'm good at, or
2. Becoming good at something new and interesting.

So the key here is that your enjoyment of a task is often heavily influenced by your enjoyment of the skills it uses. This again goes back to autonomy: if you can choose how you work on something, you can choose how much you enjoy it. This goes unnoticed a lot.

I know I'm going to enjoy a project when my boss asks me to research the toolset or framework beforehand, instead of prescribing one. It doesn't have to be big, either. I once had to write a small parser for use within a larger project. I could have used Lex/Yacc which I know and hate, but since my boss let me, I got to learn about Lemon and use that. I was certainly more motivated. Often this won't happen, but the idea scales down too.

Again, approach: if you can choose how you approach a problem, you can choose the most enjoyable route.

Purpose:

This one is a bit trickier. Whether this is intrinsic or extrinsic, however, is up for debate, so I won't say much about it. A common idea you might come across is that to live a happy life, you have to enjoy your work. Well, I believe this is largely why, and it gives you a good metric for finding the perfect job. It might be impossible, but working on things that you think will have an actual impact, or whatever other noble purpose you can appreciate, will give you a lot of motivation.

However, you usually you can't just change your job like nothing. What you can do is decide the purpose of any action you take. For example: are you doing this for the money, or the challenge, or the impact, or what? Changing your perception of a task in that way can greatly affect how motivated you are to work on it. Managing my purpose has been a key to finding motivation.

And you guessed it, the connection to approach is still so obvious it's barely worth mentioning: why you are taking a given approach is as important as anything.