To work magick of any kind, including casting a spell one must have these.
Will, Intent, and Action. These all witches and magicians should know, and will be found in all manner of operative magicks.
Will is the desire, the power of the soul and true self making itself known.
Intent is the desired outcome, the knowledge of what you are to do and what is to incur.
Action is self explanatory, being of the stipulation to bring ones self to carry out the actions and pay the piper in sacrifice.
The second set of things also of an easily identified nature. They are; Belief, Emotion, and Imagination.
For one must believe in their power, know it.
They must be emotionally invested in the outcome and power their will/intent/belief by their emotions. This is why passion, love, anger, sadness can power magicks.
And lastly, one must be able to internally envision and live through that outcome. Visualization of the desired outcome.
And the obvious one at all to make sure you aren't doing.
Don't attempt a spell that is based on mere fantasies. YOu won't be able to shape-shift, fly, throw fireballs, or any thing you might see on show. That's not what magick or spellcraft is. Magick is internal and subtle firstly, and external and notable lastly.