Magic spells are written after careful consideration of one's goals, with proper preparation, grounding and centering, and assessing the various spell components. Taking into consideration the date, astrological position and lunar phase, as applicable, one can write a personal spell of loaded intentions in either conversational style or metered poetry.
First prepare the sacred space with crystals and candles. Then channel the intention for the spell and write that on a tented piece of paper as an inspirational signpost and guide. Next, carefully choose the tools for crafting the optimal handwritten spell, such as writing utensil and type of paper. Take a moment to ground and gather energy, and call on a muse if appropriate.
The act of writing the spell is best accomplished via thought purge, just channeling ideas in free-flow format onto the page. The words can then be intuitively arranged to maximize the efficacy of the intention. Consider it like a recipe, and be sure to include any action steps that are required while working the spell at the most auspicious time in the well-orchestrated ritual. Memorizing the spell helps, as internalized words become more powerful in the subconscious and thus provide more momentum for the spell to work.
Be sure to take notes to improve spell-writing for the future. And, as always with spell-work, be sure to remove all traces of the ritual upon completion, like cleaning up the kitchen after making a delicious recipe.