Designing your own spell

Guidance already mentioned that deciding how you want it to occur is important, but I feel a need to elaborate upon that. Magick generally takes the path of least resistance, which means it can occasionally produce desired results through extremely undesirable means. For example, if you do a very generic & open-ended money-drawing spell while you happen to have a sickly relative who grants you money in their will, the universe just might decide that the simplest way to get you money is to let that family member die so you can inherit from them. A lot of Wiccans and Wiccan-influenced magicians will prevent this by insisting that it "harm none" somewhere in the invocation. That way you won't get money from something bad happening to someone else.

If you don't have a real specific goal or means in mind, the spell will still likely work, but the more specific you can be the better it tends to work. "Get me a job" will work, but not as well as "get me a job at the movie theater." The more specifically you can direct your will and energy, the more of it will end up at the desired destination (for lack of some better phrasing).

Also important, but often over-looked by people writing their own spells for the first time, is to choose attributions that you identify with. Don't get too hung up on what the "proper" attributions are, because there is no universally correct set of attributions for colors, numbers, compass directions, etc. Do some research within whatever tradition(s) you practice, keep what makes sense, and tweak the rest until it feels right to you. Many people think that pink is a good color for drawing love, but many Thelemites feel that red is a much better color for it - research both and go with the one that genuinely feels right to you. The magick will be working through your psyche, so go with the symbols and attributions that reflexively work for you.