How to be creative:

Creativity is the fiction we invent to persuade ourselves that poets are original and that authors aren't robbers in disguise.

As Barney Stinson once said on the subject of 'How to Run a Marathon': "Step One: Start running. There is no step two." The same can be applied to creativity.
Step 1: Start Writing: There is no step two. The best and most effective way to be creative in your writing is to write. Don't think. Write.

Step 2(If such a step existed): Be Completely, and On All Counts, Unoriginal: There is no possible way you will be able to come up with your own new idea, unless your new idea is stolen from someone else. Steal Stuff.
Step 3: Steal Stuff: Art is theft. Steal from the best to be the best, steal like an Artist.
Step 4: Be the Knock-Off Brand of Cereal: Be Tootie-Fruities, Cinnamon Toasters or even Krisp Rice. Be the cereal with the same ingredients as the original, but for some reason will never taste the same as it.
Step 5: MiX it UP!: Pretend there's only a little cereal left in each box and pour it all in the same bowl. Swap out milk for Orange Juice! Be DISGUSTING!

Even the opening sentence of this post is a remodeled fragment of a quote from Calvin and Hobbes. I know, it is pretty awesome, and all of you were like: "Whoa! That's a cool line! How did he come up with that?", but, it was stolen, ish. Creativity is stealing things and then changing them to fit your wants and needs. No need to waste energy in thinking, instead use your energy to write.