The big picture
I often see that developers are only interested in what directly affects their work, and they don't look beyond that to see the big picture. They don't ask the questions why the client is asking for a particular feature. They just get the task and deliver it. This often results in features that are hard to maintain yet useless to the client.
Big picture questions usually start with why. When you are tasked to develop a particular widget or feature, ask what the motivation is. More often than not, you'll be able to offer a better solution.
Think of your work like a carpenter's. When someone asks for a chair, they tell what they want, often down to the level of tiny details. But then the carpenter makes suggestions about what is possible and what is practical. After all, he is the expert, and probably already made a lot of chairs.
Do the same. When someone approaches you with a request, ask for the big picture. Consider all the aspects, make suggestions, and work with the requester towards a better solution. You are the expert.
Sometimes, it's not possible. For an API, it's unlikely that you can persuade the third party to change it just because you want to use it a little differently. But for the UI, it works like a miracle.
In many situations, your words will go unheeded, and it's OK. After all, you might be wrong, or don't see the even bigger picture. And more often than not, the status quo is standing in your way. Accept it, and move on. Small defects won't ruin the project.
The most important part is the mindset. Get into the habit of questioning the completeness of the requests and propose amendments. With time, you'll see that some of your proposals are being considered and even accepted.
This mindset is one of the differentiators that separates developers who have a voice inside the team from those who are simply referred as "resources".
Taking the initiative also builds trust. If the management sees that you care about the software and its users, they'll trust you more. Strangely, this might result in more vague specifications, but only because you'll have greater freedom to decide what is best.
And when all your proposals go unheeded, it is also a sign that you should consider switching. Usually, you'll do it sooner or later. But in retrospect, you'll be more likely to see that you shouldn't have waited for so long. Take advantage of the fact that there are plenty of work out there. And a company that rejects initiative is detrimental to your progress.
Always ask the whys behind the development requests you receive. See the big picture and make proposals how to make them better.
Treat your clients as people who need expert advice. Be proactive and suggest alternative solutions.
You are the expert. Be one whom people can trust.