1) Pick a favorite character from fiction, mythology, television, etc.
2) Change the name. Use a baby-name book or similar resource to select a name whose meaning symbolizes what you love most about this character. BabyHold and Behind the Name are good online sources.
3) Change the physical characteristics. Remove anything unusual that typifies the famous character (such as Long John Silver's peg leg), and if you wish, add something new (such as a memorable tattoo) to distinguish your character. Change some combination of the eye color, hair color, skin tone, weight, height, and other physical details. You might turn a fair, tall, slender character into a tanned, tall, muscular character with sun-bleached hair and brown eyes.
4) Consider the basic skills and traits typical of the archetype or profession then try to figure out what, on top of that, is specific to the famous character. Remove one ability the famous character is most known for presenting. Replace it with something else that your new character will be known for. Opposites can be fun to play with, but don't be afraid to throw in something totally unrelated. Think about how the absence of one key ability, and the presence of another, will shape your character's behavior. For example, imagine a brilliant detective inspired by Sherlock Holmes ... who uses intuition rather than logic to figure out what's going on, and has a terrible time convincing anyone because he can't explain how he knows, he's just right almost all the time.
5) Think of a favorite scene that showed the fictional character's nature really well. Strip that scene down to its core conflict, such as "a villain grabs a hostage and demands the hero's surrender." (Explore some sample plots to see what a bare-bones version looks like.) Briefly sketch out a setting and supporting characters as needed, taking care to vary them from the fictional example. If possible, include aspects that will challenge what your character can and can't do well -- the available solutions will depend on the hero's abilities, and those are unique to each character.
6) How will your new character respond differently to this scenario than the famous character did in the inspiration scene? Write the results. You can do this just as a short scene sketch, or flesh it out into a complete story if you wish.