Raise your standards as high as you can live with, avoid wasting your time on routine problems, and always try to work as closely as possible at the boundary of your abilities. Do this because it is the only way of discovering how that boundary should be moved forward.
Readers of this blog post are just as likely as anyone to fall victim to the classic maxim, “When all you have is a hammer, everything is a nail.” I remember a job interview where my interrogator appeared disinterested in talking further after I wasn’t able to solve a certain optimization using Lagrange multipliers. The mindset isn’t uncommon: “I have my toolbox. It’s worked in the past, so everything else must be irrelevant.”
There’s some good advice in here.