Divination can be helpful to figure out if a spell is working in a desired way. Other than that, consider what magical traditions you are working with (you might be working within a lot of wiccan or neopagan frameworks, even if you aren'tactively practicing either, for instance) and what those traditions do to ensure a spell is working or to make it more powerful. Additionally, trust your instincts. There are many ways to make a spell more potent, but perhaps you have specific things that feel like they will help, even if you don't have any research to back those feelings up.
Lastly, write down what you did. When you get results, either positive or negative, write them down. If you can't write things down, at the very least, considerwhat workedand what didn't. It will help you cast more effective spells in the future with more confidence.