Creativity is a difficult topic to have a straight answer for. It is something that is different for everyone, and is never completely surefire. It is far easier to explain how not to shatter creativity than it is to talk about how to be creative.
A surprising amount of people completely disregard the basic principals of psychology that allow people to be creative. The first and most important thing to do when trying to be creative is do it for your own good. While this does sound somewhat strange, any sort of extrinsic motivation (even indirect) can be a creativity killer.
In Daniel Pink's fantastic book DRiVE, Pink references a study from Teresa Amabale back in the 1970's. Essentially, she hired a large group of professional artists to participate in a study. Along with the artists, she hired a board of professional art critics who had no idea that they were even participating in a study.
She had the artists decide on a collection of commissioned and non-commissioned works, but gave almost no artistic direction as to what the artists could create. Some of the artworks were just paid for (the commissioned).
So, all of the artworks were finished and Amabale took them and had each one critiqued on a scale of "creativeness" and "technical skill". The art critics had no idea that they were part of a study, or which art was commissioned.
The results? The artwork that was commissioned was rated consistently
less creative than the non-commissioned works. However, the most interesting part is that the technical skill was rated the same across the board.
So what does this say about magic? While the tricks you create with extrinsic motivation in mind (any form of reward, being money, publishing or good feedback from others), the creativity is consistently less.
Another point that has been proven time and time again is the feeling of primary use. The magic that is often considered "better" and "more creative" across the board is that which uses objects and principals in a way for which they aren't typically used.
Karl Duncker had interesting experiments about this in 1945. He had hundreds of people participate in a study where they would enter a room. In the room, there was a table and a cork board hanging on the wall. Karl would present each participant with 3 things: a lit candle, a box of tacks and a book of matches. The challenge was to somehow adhere the candle to the cork board without letting the dripping wax touch the table.
Many people tried tacking the candle to the cork (which didn't work). Others attempted to create a "tack cradle" for the candle (which also didn't work). Eventually, it occurred to the participants that if you emptied the box of tacks, you could tack the BOX to the wall, and stick the candle inside. It would stand up and the wax wouldn't drip to the table.
A relatively simple solution (simplicity is considered VERY good in magic effects) but one that is not typically considered because that is not the box's primary use. When creating magic effects, look at each object (and each part of each object) in terms of what it can
do and not just what it does.
Those are two tips in creating great magic effects (or, moreso, not creating bad effects). There are some excellent resources on the subject though. Jay Sankey's Create Your Own Magic DVD is excellent in terms of how to inspire yourself, but does little in the way of informing you on what to do to be creative.
My advice (which may not be everyones) is to study creativity theory. Once you know the theories on why creativity works, where it thrives... etc, it is much easier to actually be creative. Creativity is an art, so it is difficult to become better by study, but studying WHY it works can be effective in attempting to create situations in which you create the best magic that you possibly can.
I recommend reading Flow by Mihaly Csikzentmihaly, DRiVE by Daniel Pink, Predictably Irrational by Dan Ariely, and if you can find a copy, The Nature of Creativity by RJ Sternberg (which actually references Teresa Amabale and Mihaly Csikzentmihaly on numerous occasions).
Just my two cents.