Eliminate negativity. The thing that will hold you back from thinking outside the box more than anything else is negativity. Consistently telling yourself that you can't think creatively or vetoing every idea as too "out there" is going to severely limit what you come up with.
Consider what it is that you tell yourself about your ideas. When you come up with that amazing book idea do you immediately think "I could never write that?" That is a surefire what to ensure that you never do write that.
Whenever you find yourself responding negatively to your ideas, replace the negative thought with a positive or neutral thought. For example: if you found yourself thinking "I'm never going to be able to entice advertisers with these incentives" stop yourself and say "I'm going to test out how these incentives work to get us better advertising faithfulness."