Be yourself. Be prepared.
In an interview situation, nothing damages your confidence more than pretending to be something you're not. You're trying to keep the story straight in your head while under pressure and they're basically interrogating you. And if they smell a rat, they'll find it, that's their job. It's not good.
And the worst thing about it is that they might actually want you, not the perception of a person that you're putting out there. You might not get a job that you'd be a perfect fit for. Or (worse, in my opinion), you might get a job that you're a poor fit for and be miserable.
Take your last question, for example: How were you able to improve productivity in your projects?
Are you an agent for change? Can you demonstrate it? It's actually ok if you're not. If they have a team full of agents for change already, they might just want someone who'll quietly work their asses off and not complain that they could do more if the coffee-maker was four inches closer to their desk and the carpet had a thicker pile.
There is a whole spectrum of "agent for change" that ranges from "I just get on with things" to "I will throw chairs around the office to get a process changed." You don't know which part of the spectrum they're looking for (probably neither extreme), so don't try to guess. Just be yourself and let them decide if you're the person they're looking for.
With that in mind, though, it's worth looking around the internet for standard interview questions in your industry, or even going to interviews just for experience, then thinking about the best answers that explain to them who you are.
"Heh, to tell the truth, my recent teams have been full of people who fight over processes, ad nauseum, and honestly I haven't felt the need to get involved. But, if I was on a less-forceful team and I felt something in the process was slowing us down unnecessarily, I'd write up a short business-case for it, pass it around the team to see if they supported it, and then I'd present it to my boss, as a complete solution. I mean, no one wants to hear about problems, right? Just solutions."
Boom! You've not really answered the question, because you don't have an answer, but you have let them know who you are, what you'd be inclined to do in that situation AND you've shown a bit of empathy towards managers in the process. They love you. You're hired.
But that's just one example. The point is to be prepared for most questions, and be ready with answers that tell them who you are. The more prepared you are, the more confident you'll be. If they then come up with a question that you haven't considered already, you can confidently smile, say "That's a GOOD question," and take a moment to think about it.
You'll be so well-versed in coming up with answers by that point that you'll be less likely to draw a blank.