When faced with an error/bug, I have seen a lot of people wasting time trying to second guess it or aimlessly googling for it. This should be your last resort.

1. Check your logs. Almost all applications have a log where it will write it’s errors. If no log is present, try to see how you can configure it for your application/framework.
2. If the application itself is crashing, check your syslog. If there is a segfault, it will be logged in your syslog.
3. Read the api. Many people tend to use apis without even moving their eyes over it.
4. Read the spec. For example, if your web.xml in a war file is throwing some errors, read the servlet spec associated with it.
5. If your application itself is not starting, read the readme file that usually accompanies any application. It might give you pointers on what is the problem with your set up.
6. Learn to use a debugger properly. In fact, your should be a master at it.