I have several methods but the one that I tend to use the most is to decide what would fool the pants off me, and then work my way backwards to figure out how I did it. One of the routines I have developed is an international reverse matrix, standard reverse matrix but using a half dollar, copper coin, chinese coin (with hole) and £2 coin (and no extra coins). The reverse matrix has been my favourite coin routine ever since I saw Roberto Giobbi perform it in the early 80's. I wanted to make it even more impossible whilst looking as clean as the version Robeerto won FISM with. My methodology is that I start from the completed trick and work my way backwards, hard to explain but it works for me. I'm at the end and I ask right how did I get here? I then gradually backtrack through the routine untill I get to the start. Funny enough though once I've got to the start and I know how to do the effect I then go forwards and see if I can tweak it and add some kickers. I usually use this method for creating a new twist on an old idea or for making a great routine more impossible (and usually aimed at other magicians rather than lay audiences as laymen will be just as amazed by the french drop as they are by a raven vanish if it is performed properly, either way a coin vanished). My current project is a coin version of open travellers card routine (not to be confused with the matrix type open travellers coin routines).
I guess the reason this method works so well for me is because psychologically I am starting from a position of success. By starting from the end and working backwards I have already accepted that the method exists and it is just a case of finding it. Whereas if I start from the beginning I don't yet know if it is possible to get to where I want to end up. Best analogy I can think of is that if I were to blindfold you and take you into the middle of nowhere, sooner or later you'd find your way home, but if I were to tell you I was waiting for you in the middle of nowhere you may spend a lifetime looking and never find me
My other method is to let my mind do the work for me. The brain is an incredible piece of kit, and is one of the best problem solving machines known to man. Whilst your recall may not be perfect your memory is exceptionally good, your brain has every moment and every experience of your whole life stored. If left to its own devices the brain will search through that huge database and will find what it needs. How I use this to my advantage is to feed in the required paramaters then let the brain go away and find the answer. To do this spend some time concentrating hard on the requirements, ie needs to be simple, needs to be eye catching, must use everyday objects, will be performed standing etc etc. After spending a period of about 20 mins concentrating hard on the requirements I will then forget about it and let the brain go and search through it's storage for something that fits the requirements.
An example of this in action was some years ago I needed a big finish for a close up act. It had to be snappy, unexpected, visual and most importantly easy (I was running out of time

) It also needed a witty patter line so that I could finish nicely. After focussing on these requirements quite hard I went to bed and forgot about it. Shortly after breakfast the next day it hit me in a flash, 3 small hooks on the back of my close up pad, a bottle of Schweppes tonic water hanging from each hook by small loops of fishing wire. After finishing my last routine I lift the back of my close up pad pivoting the pad towards the audience (P / I) (imagine the P is the audience and the / is the close up mat and the I is me (viewed from the side oh and I'm taller than the I

) tipping the coins off the mat (and bringing the bottles up to the table). As I do this I say "After performing these little miracles I am often asked who taught me to do magic" At this point I slide the mat to the right (which unhooks and reveals the 3 bottles) and say "Sshh !! You know who" (Hehe that advert and the line was well known in those days".
Ok I know I just revealed a secret but as it is one of mine and I haven't used it for years consider it a freebie

although if the mods want to remove the explanation on principle go ahead and do so (but I'd appreciate it if you pm me a copy of the unedited version first to save me typing it at a later date when I have access to the secret area

)
Hehe what started as a quick reply turned into an essay, my apologies, I have a habit of doing that, I talk too much in real life too
Mark