Professional writers, on the other hand, have no excuse. Presumably you've been through your draft more than once. If not, you should have been. Otherwise, there will likely be major holes in your story, in addition to grammatical errors.
Here are a couple of errors that I particularly hate (and yes, I know the bullet points are not complete sentences):
- "between you and I" -- that's just incorrect
- "taller than me" or "older than me" -- again, just incorrect
- "tell Sue or I" -- I'm starting to sound like a broken record here...
- "lead" is not the past tense of the verb "to lead;" it's "led"
- not understanding comparative and superlative forms of adjectives (noble, nobler, noblest versus beautiful, more beautiful, most beautiful, but not "more noble")
- using the word "weary" when you mean "leery" or "wary" (the first one means "tired" whereas the second and third mean "cautious")
- subject-verb disagreement, especially with compound subjects (it's "the cookies and milk were delicious," not "the cookies and milk was delicious")
- using a mix of British and American English; I don't care which one you use, but pick one and stick to it
Bottom line: everyone knows someone who is good with grammar. Have him or her read your work and correct it. If you know this is one of your weak areas, frequent the website linked to below, or others like it on the web:
If you need more information about proper use of punctuation, you can also pick up a copy of Eats, Shoots & Leaves by Lynne Truss, though be forewarned that it highlights some rules of English punctuation that are true in Britain but not in the US (rules for commas in lists are different, etc.):