What's the number one thing I notice when reading Wikipedia articles about our fine traditional fantasy authors? Plagiarism.
As in "man, what a Tolkien ripoff" or "this guy played too much D&D" (Licensed products notwithstanding). Most people also seem to get stuck on that same issue everyone notices: Places and people have names that are similar to what appeared elsewhere.
Here's my take: It's hard to be completely original. For example, with Avarthrel, I could have started doing completely original fantasy stories. Yet, I felt that was not the way. When reading "original" stuff, I've frequently seen stuff that's too strange to my senses. (Example: Computer game The Elder Scrolls III: Morrowind. Many familiar elements, yet most of the stuff in the game makes me look at that and squeal "now what the heck is that?") I wanted to use many "traditional" fantasy elements. And with that, I have to hang a plaque on my door that says "Writer of Fine Archetypical Myths".
The point is this: There's a fine line between plagiarism and using some common familiar elements from other stories. The "modern fantasy" would not have gotten too far if people had not been ripping off Tolkien to small extent; Everyone knows what elves are, yet Tolkien's elves aren't D&D elves, which aren't Elfquest elves. Nor are D&D drow really the same as Feist's moredhel, for example.
This entry was mostly sparked by one Avarthrel point - yes, I'm going to have to put elves to the next story somehow. The question is, how to avoid clichés, yet embrace them?
Also, I could go on and on and on about "name plagiarism". Try to invent, right of top of your head, a couple of dozen funny-names for fantastic cities. I bet people have used something already that's 95% same. Take something sufficiently short that sounds Elvish and rolls off the tongue and bingo, someone probably has used that already. Heck, it happens with human names. (I cringe every time I hear "Mara" used as a female name. Our previous president was a guy!)