A fountain pen can change anyone's handwriting into something resembling calligraphy. Fountain pens, or calligraphy pens, are available at most craft stores and don't take long to set up. Modern fountain pens usually have detachable nibs so you can write in different sizes and styles. If you have one on hand or can borrow one from a friend, fountain pens are a quick, free way to spice up your handwriting. However, fountain pens may not be a good idea if your writing is messy to begin with.
If you want to do a complete overhaul of your handwriting to make it look creative, find some artistic and creative fonts. Font websites such as 1001freefonts.com have a plethora of fonts available to get you thinking. Find several fonts that you think look good, then apply them to your handwriting. Go through your handwriting letter by letter and tweak each one. For instance, you might want to use a Celtic font for your lowercase d, curving it up and around instead of giving it a straight stem; or you could use an Old English S.
Most people write in either cursive or print. Each style can be interesting in itself, but when you combine the two, you get a truly unique handwriting. Decide what letters you want to write in cursive and what you want to write in print. A lowercase z, for instance, looks more interesting in cursive than in print. Y and g also have fun cursive forms that look good in print surroundings. Use a system, though -- don't alternate every letter, or your writing will be merely confusing.
You don't have to change your entire handwriting method to give it a unique touch. Writing with unique and interesting capital letters will give your overall writing a different flair, and it's easy. Capital letters don't occur very often compared to lowercase ones, so you can make your capital letters as ornate as you want without sacrificing readability.
Try adding a spiral at the bottom of your large G, or put a dot or circle in the middle of your O. Bring the last stroke of an M or R down below the line. Add serifs, or use giant lowercase letters for your capitals. Get a piece of notebook paper and practice, then when you have what you want, start using it in your everyday writing.