There could be many reasons why a spell may not work. It could be because the spell is "fluff"'made. Fluff spells are created by inexperienced practitioners that often have misconceptions about magic and a through thorough understanding of it. Usually, these people come up with spells that are purely fantasy and fiction.
In order to cast a spell properly, you need to at least have some basic understanding of how magic works.
In addition to what Personified said about the basics, I recommend that you go to the following links:
Newbie Central: http://www.spellsofmagic.com/newbie_central.html
SoM Survival Guide: http://www.spellsofmagic.com/coven_ritual.html?ritual=1944&coven=1
Afterwards, you should search for and a join coven on this site that appeals to your interests and what you wish to learn.
People these days don't have time to personally teach you. That is why covens on this site were created.
Good luck and blessed be.