Writing your own spell down when you have enough understanding of how magick works is the best way to have a successful spell.
The reason is when you write a spell, the spell becomes bound with your energy and it carries a piece of you. So it has a better chance of success. Just as a security code which only works with your voice.
If you're a beginner, take a look at all the FAQs as everything generally is explained there. Before attempting to cast a spell, embrace the definition of real magick and then start writing your own spells.