So here's a tip that frankly I'm not to fantastic at myself.  Try and keep a small notebook with you no matter where you go.  Something perhaps that can fit in a pocket and you can use to just quickly throw down an idea into.  I have a couple notebooks that I use to do exactly that, though I'm not as diligent in actually carrying it as I should be.  Inspiration is extremely fickle, in the very best of times.  There will be days, weeks, or even months that ideas will just come to you without stop.  On other occasions though, not so much.  But you can't always just sit around waiting for inspiration to strike, and if you think an employer is going to just let you sit around waiting for it to strike you then you're out of your mind.  A notebook though, should be able to at least catch those moments of inspiration the best you can.  Maybe every idea won't be exactly what you need but they very well lead to an idea that you can use!