Although I have been a Wiccan for around a decade and a half, I have cast less than a handful of spells. I am of the opinion that Wicca is a spiritual path that, while not incompatible with spells, is complete without it.
I find that most methods of spell casting to be too much “in our heads.” We gather items to fit our purpose based on long lists of correspondences that were copied from books. We use items we have purchased and have not formed a personal connection with. And often we call upon deities that we have had little interaction with in the past, and who we may never call upon again. The whole process seems very contrived to me. It ignores the elements that are always present in our lives, and seems to be about creating something new for the sake of newness.
It can be argued that magic works only when performed in an environment that is “set aside” or is special in some way—within a Circle or other ritually prepared place, for example. It can also be argued that the only correspondences that are valid are those that have been discovered by adepts and passed down through the centuries. I disagree with all of this. To me, magic is not a matter of spells and ritual, but og everyday actions and focused intentions.
First, I make use of personal correspondences, and thoroughly examine any others I choose to use. There are some, like the assignment of birthstones, which I essentially accept as is (although, these have changed over time due to the influence of the jewellery industry) because of the cultural weight behind them. But most other correspondences I research to make sure they work for me. For example, the colour purple is commonly used for business dealings, communication, writing, and spiritual development (to name a few aspects), but because purple is my favourite colour I feel it is appropriate for me to use it for relaxation or meditation.
When it comes to the items used in magic—be they for focus, sacrifice/gift, or otherwise—I do not use them. I am my own focus and my own gift to the deities.
This brings me to the gods called upon when performing magic. I want my magic to be as natural as possible, so I do not call upon deities with whom I have never worked. I find that I need to cultivate a relationship with a deity, through study, worship and meditation, before attempting to ask for help while working magic. Anything less and I feel that my probability of success would be severely diminished.
I think the success of your magic ultimately comes down to a two things, props and correspondences and all those other traps aside. First, the only way that your magic has any possibility of succeeding is if you truly, down to your very bones, want what it is you are working towards. And second, your actions must be true to your own moral code. Neither of things guarantees success, of course, but they are the way to forge a path towards your goal. Anyone who wishes to seriously work any form of magic and have a chance of it being successful must have a deep knowledge of their self. This is knowledge more useful and more powerful than any correspondence chart will ever be.