Here are some common mistakes that begginers make during spell casting:
1)No meditation: This is one of the biggest mistakes. Don't take power of meditation lightly, it enhances your magical skills. It helps you to focus on the spell and its purpose. Without focus spells fail.
2) Thinking about the spell after casting: Don't keep thinking about your spell after casting it. If you keep thinking ' will it work?' 'When will it work' and so on you will not let your energies to go into the universe and make your spells fail.
3) Stupid reasons: Don't cast spells for stupid reasons. Cast spells if you really mean it. Magic is not something that you can play with.
4) Believe: Belief is the most powerful tool in magick.