A pen pal of mine recently told me that she'd bought a bag of 'graveyard dirt' from an online auction site.
My first thought was, "Yeah, I'm sure that's from a real grave (!)".
My second was, "Well, if it is, which grave was it from..?"
Now, call me a superstitious little witch, but I would not buy a random bag of dirt to use in my spell casting without knowing where it came from. In fact, as I recall, my friend said that the seller was advertising it as something to help 'summon the spirits for protection purposes'.
I can see it now:
"Right, let's use dirt from the grave of an unknown person, who hopefully wasn't a murderer or mentally unbalanced during their life, and call upon their spirit to help us. And we won't offer any thank-you at the grave in return."
Note the careful use of sarcasm there.
My friend was a bit wary of using it after that comment, oddly enough.
Spell casting is, as I do it, a much more personal thing. If I felt the need to ask spirits for protection, I'd call upon friends or relatives (who I knew would be likely to have an interest in me - and no psycho tendencies) and leave something they'd have appreciated in life at their graveside, as a thank you.
Rather that, than invite an unknown entity into my home.
Or a bag of plain dirt. There's loads of that in the garden and it's free!
Know your sources.
The same applies to other aspects of spell casting and creation. Know where you're getting the information from - check it and even double check - make sure it feels right for you, and only then get on with it.
If you find a piece of writing, spell or poem that you feel is perfect, then fair enough, it's OK to use it. Otherwise, write your own, because reading out words you don't believe in is a waste of your valuable time and breath.
If you can't pronounce a deity name or are unsure about their aspects and traditions - don't involve them in your work. If the name means nothing to you or you're more worried about saying it wrong, it will jolt you out of the 'concentration zone'. Not to mention how impolite it is...!
Seek out things that resonate with you personally. When researching something, learn not from one book or author or web page, but from as many as you can.
Then amend, re-write, recycle, and try it out. Remembering to make notes, so if works well, you know what does. And vice versa!
We have many moots and pagan gatherings these days, where you can swap ideas or ask for advice. Don't be embarrassed about asking. Many people don't work in a group or coven environment, and moots offer an informal meeting of minds. Well, until the bar closes...
The internet is a huge - if variable in quality! - source, where you can find things to inspire you, but once again, check and double check the information. Yes, that's a lot of cross-referencing!
But don't take one person's word as the law.
Not even mine.
You never know; those bags of dirt for sale may actually be from graves.
However, if any of the hills in the local countryside halve in size, don't say I didn't warn you!