The general strategy[1] is to make sure what you're designing fits into an existing design pattern. It should be rare for you to have a situation where you're not within the confines of a well-known, well-understood design pattern. The sooner you become familiar with patterns, the more rapidly solutions that fit those patterns will come about in your head. The solutions will also feel less ugly, since you're essentially still being conventional.
You should be able to describe, in English, what design pattern you're using to come up with a fix.
[1] I didn't say this was a perfect strategy, but I think it helps.[2]
I wanted to second this comment. I really like the concept behind this project and will make an attempt to put some effort into looking into it.
One of the biggest positives of this service is that you can keep your own data. A year or so ago, we had some constraints where we didn't own the data we were analyzing and were not free to use web based services to dig into it. This was a serious problem and I'm glad plot.ly is attempting to address this in the enterprise product.
If you live in California, you should do nothing but visit all the different state parks and the small towns in between. Take a car, some camping supplies, and maybe a laptop and just go. Travel light.
If you do things right, you can pretty much consume the entire 2 months doing this.
This is an easier question to answer if you've ever worked on some open-ended research or problems where the path to the solution is just not known. Those sorts of problems seep into your dreams even when the last thing on your mind is work.
However, even if you aren't doing research, good answers are probably found in those scenarios where you are pushing the limits of some particular software framework. Anywhere you have to bend the rules or invent new rules just to accomplish something makes for a good interview story. How detailed you go in your answer depends on how entertained the guy on the other side of the table is.
The general strategy[1] is to make sure what you're designing fits into an existing design pattern. It should be rare for you to have a situation where you're not within the confines of a well-known, well-understood design pattern. The sooner you become familiar with patterns, the more rapidly solutions that fit those patterns will come about in your head. The solutions will also feel less ugly, since you're essentially still being conventional.
You should be able to describe, in English, what design pattern you're using to come up with a fix.
[1] I didn't say this was a perfect strategy, but I think it helps.[2]
[2] Well, it helps me anyway. :-)