Common pronunciation errors for Anglophones

[Cheiromancer]

I am a native speaker of English (I grew up in Alberta, to locate the accent more exactly) and there are a few issues that I try to pay attention to when I pronounce Greek. For instance, I try to avoid lengthening short vowels in open syllables, and to not voice sigmas between vowels (but I do voice them before voiced consonants). Getting the aspiration right in stops is hard (tau and theta, phi and pi). I'm sure I'm missing some.

What other mistakes should an English speaker be sure to avoid?

[Markos]

What other mistakes should an English speaker be sure to avoid?

North Americans English speakers tend to "glide" vowels almost to the point of adding a "y" to the end. We also have a tendency to replace short, unstressed vowels with a schwa. There is sometimes inconsistency in how we pronounce iota: ὅστις like "pit," but ὅτι like "feet." We tend to conflate ἔβαλλον and ἔβαλον.

I would not call these mistakes, by the way, but rather dialectical variations.