Two useful flags you can specify when comparing files are -b (ignore blanks) and -i (ignore case).
You can use them separately or in combination. The ignore blanks feature is especially useful when you’re comparing the source code for two programs, since indentation changes are rarely significant. For example, here’s how you might compare two program files, ur2cool.c and ur2cool.backup:
diff -b -i ur2cool.c ur2cool.backup