You do need to know what you're doing in order to begin with practicing witchcraft and magic. After you finish with a solid foundation, things will have a bigger potential to successfully work. Everything needs basic knowledge.
Here's a recommended link to the basics (guide for beginners):
If you have done this, and you already know what you are doing you can start to cast spells.
And now the last thing that might be helpful...
Tips, recommendations and optional steps (associated with spell casting).
After you know about the important things and stuff you must follow, you can keep in mind that there are other tips and recommendations that might make your spell to be more effective and use its potential ! Everything has options that are meant to make everything more effective. But remember, this is optional.
So I recommend you to check out SoM's " Tips " tab, which talks about this sort of information. (moon phases, materials and supplies , mental condition , planetary hours and days , colors , etc) :
Besides that, there is an expended thread here about the basics which you can find here:
Hope it helps.