This is how I view spell crafting. If anyone disagrees with something I say, please tell me, and explain your reasoning. If you do not explain, how can anyone learn? And learning is the point of my writing this.
Part One: Writing
When writing your spell, you need to keep the following things in mind:
1) The phrasing of the spell.
2) The literal meaning of the words you use.
3) The figurative, or symbolic, meaning of the words you?re using.
1) The phrasing is important, as it determines accuracy. For example, you use as your spell the following sentence: Love will come into my life.
Right away, we have several major problems.
First, you fail to claim when love with enter into your life. As such, it could be the next day, or the next year. More importantly, you will have no idea if any love that comes into your life is a result of your spell, or a result of fate or coincidence.
Second, you say not what form of love you wish to enter into your life. By using this spell, you could very well curse yourself with unrequited love, thus leading you to love someone with whom you will never be. Or, this spell could cause you to meet someone new, who shares love with another. Thus, love would be brought into your life, but you would not benefit from it.
2) Next, look at the literal meaning of each word you have used. For example, you use the following phrase as part of your spell: Steal from him joy, till at last it is that he stands at my side
In this context, your spell would take form your target any joy he would naturally feel, and give it to you. Yet the transfer of joy would be unlawful, morally wrong (for the word steal means to unjustly take) Worst yet, a literal interpretation of this spell means that once the target stands at the caster?s side, the spell (or at least part of it) is void, no longer valid.
Literal meanings of words are important, both in use and understanding. For if you understand the definition of each word, you can better insure you use the proper phrasing, and thus help avoid mistakes. In addition, by knowing the literal meaning of a word, you can better craft your spell to fit your needs.
3) Lastly, you must look at the symbolic meaning of the words you use. Dove, literally, refers to a type of bird. Yet it is a symbol for peace, and it is a sacred animal of Aphrodite (Thus, if you are a Hellenistic Pagan, a Dove would symbolize love, or a peaceful love.)
By using symbolism, you can add a more abstract power to your spells. If you can find a word that means what you need it to, and also symbolizes something that holds reference with regards to you desired goal, your spell will be more useful.
In general a long spell would hold more power, because it would have the complexity needed to both ensure accuracy, and a large basis for abstract power. However, long spells present a problem: The longer the spell, the more difficult it would be memories. If this is the case, the caster would have to read the spell while speaking it. Doing this splits concentration, making it more difficult to complete a spell. As a result, the caster may lose the needed focus, resulting in a complete, or partial, failure of a spell. It, therefore, is important to balance length, complexity, accuracy, and simplicity.
Part Two: Miscellaneous.
As you write your spells, also consider what items, if any, you plan to utilize as you cast your spell. Decide if you wish to make reference to your object within your spell (With this candle, tall and red, I now fill with) or do you simply use it. If the latter is your choice, you need to decide where in the spell you wish to employ your item.