Here, I am going to attempt to help anyone that is having any difficulty in spell casting. I apologize in advance for any misinformation and encourage any correction and constructive criticism.
1. The basics are important. Before casting any spell, you should have knowledge of the basics. These include, but are not limited to grounding, centering, shielding, visualization, and circle casting. There are many posts here on SoM that can help you to understand all of the basics and any tips to perform them at your best. Practice every day, until you know you can do each well. When you feel you're ready, then you can cast your first spell. Keep in mind you should start small if you're just getting into the work.
2. Intention. Intention is a very important factor in a spell working. If you are just saying to yourself that the spell will work but don't actually really believe it, chances are you are not going to get results. Your intention must be clear and you must know what you want.
3. Outrageous spells. If you're wanting to do a spell that will make you sprout wings, turn you into something you're not, then those automatically will not work and are considered "fluffy". When looking for spells on here, keep in mind that those kinds of spells are ones you should avoid. It is most likely better for you to write your own spell, that way you can shape it to your liking, and because words written by your own hand have a better chance of working.
4. Moon Phases, Elements. I've come to understand that the moon phases and the elements really aren't considered part of the basics anymore, at least from what I've seen. However, if you do work with the moon phases or the elements, you may have becomed accustomed to it as a routine when doing any spell work. When you don't work with them, say for one spell, you may have the thought that the spell won't work as well as it would if you did and having that thought would be sort of a "placebo" which would lead to the spell not working as well if you think this. Now again, many might not do well with moon phases or work with the elements, so this is just here for the people that do.
5. Supplies. Remember that not all spells need supplies, but if you are having a spell that needs specific ones or you have made a spell that you have supplies needed for, it is a tip from me to have the supplies you need to ensure a greater chance of working.
6. Concentration. Remember to always concentrate on your spell, and to bar out all external distractions.
7. Writing your own spell (as a tip, not required). As a suggestion, I encourage you to write your own spells and learn how to do so effectively. When I write my own, my words are easy to understand so that I may understand what I have written as well. You don't have to make it fancy. This is your spell and you can have it as long as you want or as short as you want or with no words at all. Also remember that not all spells need to have words.
I hope this was able to help, and I hope most of my information was accurate, this comes from my own understanding.