Looking for many possible answers rather than one.
Allowing yourself to make wild and crazy suggestions as well as those that seem sensible.
Not judging ideas early in the process - treat all ideas as if they may contain the seeds of something potentially useful.
Allowing yourself to doodle, daydream or play with a theory or suggestion.
Being aware that these approaches necessarily involve making lots of suggestions that are unworkable and may sound silly.
Making mistakes.
Learning from what has not worked as well as what did.