1.) Learn what is and what is not possible. Anything that says it change your dna in the physical world is a lie. No wings, no fins, no fairy, no vampire, no mermaid, no demon, no half dragon, no demigod, no gender change (without surgery), etc.
2.) "The basics" meaning grounding, centering, and meditation. Meditation can help you achieve a relaxed state to be in the right frame of mind to cast a spell. If your upset or emotional many believe that this can influence and effect a spell for better or for worse. Emotion can put energy behind the spell. But if your feeling angry and trying to do a love spell, that sounds like a disaster! Centering is also important because finding your center and breath control is what I would consider essential. Grounding is a good idea because it can help get rid of excess energy. Visualization is also important for spells but that one I think is rather obvious and as such doesn't need much explaining.
3.) Though religion and magick are not the same and magick can be done in any religion and with no religion at all, it can still be of benefit to understand some basic religious principals. The reason being it might dictate how or what you cast. For example, if you believe in karma it might effect your view on things. Also, many people mistake Wicca which is a religion for witchcraft. Sometimes evoking a deity in spellwork is done. But it would be wise to know the deity, what culture they come from and the religion they are associated with.
Please understand that all of these are very brief ideas and concepts that go so much further in depth. If you google any of these subjects or look further on this site you will find many informative posts on them. You can also google free pdfs of books or find a lot of books on the subject cheaply on Amazon. There are many in depth tips and exercises you can do. I would add links but they would be endless since the question is very vague and open ended. I hope this has helped you.