The late programmer, entrepreneur, writer, political organizer, and hacktivist Aaron Swartz (1986–2013) wrote years ago a great essay about productivity. The whole piece is worth reading.
One of the things he proposes to spend time more efficiently is to choose good problems to work on:
Life is short (or so I’m told) so why waste it doing something dumb? It’s easy to start working on something because it’s convenient, but you should always be questioning yourself about it. Is there something more important you can work on? Why don’t you do that instead? Such questions are hard to face up to (eventually, if you follow this rule, you’ll have to ask yourself why you’re not working on the most important problem in the world) but each little step makes you more productive.
This isn’t to say that all your time should be spent on the most important problem in the world. Mine certainly isn’t (after all, I’m writing this essay). But it’s definitely the standard against which I measure my life.