Writing down your intent is one of the clearest ways of, well, spelling it out to the universe. But how? A quick search will reveal several takes on what a "magickal" alphabet is, but which is best? That will all depend on you, for myself, the answer is none, and this was just confirmed by another wizard friend of mine.
Any pre-existing alphabet will have its meanings already set. Each character means whatever it means, it will carry that with it when you use it, it will already have that "vibration" (uhg there is that word again!) to it. These can be useful enough, if the pre-existent meaning is what you need, but what are the chances of that always being the case?
The best alternative is to make your own alphabet. This will take time, yes, but your results will always be exactly what you mean them to be. As someone who is minorly obsessed with etymology, trust me when I say that the origin of a word can change your opinion of it entirely. Don't believe me, just look up the word feisty. The only way to always mean what you want, is to make it yourself.
When you write your alphabet, think about what shapes mean and imply to you. I recommend creating characters both to replace the letters of the alphabet you use for when it cannot be avoided, but also ones to mean things you are most likely to use. My first ones were words such as life, protect, health, care, safety, abundance and freedom, as well as ones to symbolize people. I created a semi-circular way to write it so that it is fairly flexible, but essentially I am left with a paper that simply LOOKS magickal, but no one else can read it, which is its own benefit. Mind you, I do borrow from other alphabets when it is appropriate, but I will not be limited by such, and I suggest you not be, either.
Speaking of borrowing others alphabets, I am hoping to convince my wizard friend to guest write about a sigil he created, and perhaps even explain about casting apple, so keep an eye out for that- perhaps you can help me intend that to happen.
Yes now I am getting silly, and getting off. Good night and good morning.