1. Sprinkled Apostrophes

   There's a giant in the sky with a salt shaker full of apostrophes. He shakes, and where they land, they stay. If he misses an appropriate word, that one does without. His favorite target is public signs, but the second choice is websites. Writers need to be clear on plural versus possessive nouns and pronouns, and stop committing atrocities like, “There were two house's for sale on that block.” Babie's makes me crazy. Her's does, too. Let's not forget the unnecessary ones in abbreviations like CD's and DVD's (correct CDs, DVDs)
   

2. Confusing Which, Who, and That

   It is acceptable in English (though I disagree) to refer to your dog as a pet that likes people. It is not correct to refer to people as that: Instead of “The man that was in line in front of me,” making him an object, say, “The man who was in line.” The word which is often erroneously used in place of that. Use which when the meaning of the sentence would be incomplete without a following phrase. Otherwise, use that. “The house, which needed work, sold for much less than expected.” “The house that needed work sold for less than expected,” means that house as opposed to the other one that didn't need work.

3. Comma Splices

   A comma splice occurs when two complete sentences are strung together, connected by a comma without a conjunction. “We went to the store, we bought milk,” could be correctly written, “We went to the store. We bought milk,” or, “We went to the store, and we bought milk.” Comma splices of three or more sentences strung together make me as crazy as apostrophes tossed into plural nouns.

4. Misplaced Modifiers

   Our writers' group calls these "walking privies", because the first one noted by the group was, “Walking across the clearing, the privy appeared to be old but in good condition.” Of course, only in the fantasy genre do privies walk. The most common error I see is a gerund phrase like the walking privy that has no word it is intended to modify at all, let alone one following the gerund phrase. “Having said that falls short of what it should do.” Having said that cannot be a subject. In this case, the writer should have followed the gerund phrase with a subject. “Having said that, the measure falls short of what it should do.”.

5. Misplaced or Omitted Commas

   Looking for a massive dose of confusion? Try sorting out the changing use of commas. However, some rules remain firm. Always use a comma when directly addressing someone, as: “Hi, Ann.” Use a comma when combining two sentences into one with a conjunction. “We went to the store, but we didn't buy milk.” Do not use a comma when combining sentences with a conjunctive adverb, such as “however” or “nevertheless.” Instead, use a semi-colon. “We went to the store; nevertheless, we didn't buy milk.” That rule, however, doesn't apply in this sentence. The adverb conjunction “however” is not joining two complete sentences.

6. Tense Shifting

   Writers do intentionally shift forward and back in time, but we need to be sure the shift is intentional. When a piece is in the present tense, it is disconcerting to the reader when our subject suddenly does something in the past without a transition to the past. “The team huddles around the Quarterback, who was deciding the next play.” Conversely, “The quarterback intended to throw the ball to Joe, but then he changes his mind and throws it to Dan,” is equally incorrect.

7. Mismatching Plurals

   It may be a political correctness problem that requires re-writing, but it is still incorrect to say, “The clerk who did this needs to get their act together.” The clerk is one person. Their refers to more than one person. To compound the error, needs is a singular verb, and cannot refer to “their.” His or her act is clunky, but their act is just plain wrong, and appears everywhere.

8. Modified Adjectives

   You have to appreciate the humor in modifying a modifier, but we are developing a habit of saying something is very unique, a physical impossibility. Unique means one of a kind. How much more unique can you get than one of a kind? I will readily believe that an object is more unusual, or more rare, but I'm still waiting to see anything more unique. Or more complete. More perfect. More unanimous. Less absolute. Less fatal. For these terms was the word oxymoron invented.

9. Misplaced Adjectives

   Especially applicable to "ly" words, the misplaced adjective can confuse the entire meaning of a sentence. Consider, “Angela only wrote three poems for the anthology,” versus, “Angela wrote only three poems for the anthology.” In the first instance, is it possible that Angela wrote three poems and one essay? Or did she write nothing but poetry?

10. Fragment Sentences

    There is a category called stylistic fragments, incomplete sentences intentionally used for emphasis. These are effective tools for dramatization. Badly used, or used in a string that would sound the same if spoken aloud, fragments are merely incorrect. “He lives on the water. In a houseboat,” is meant to be read with a slightly different emphasis than, “He lives on the water in a houseboat.” “He lives on the water. In a houseboat. When he's home,” would be better written as a single compound sentence, since it is not intended to be pronounced with particular emphasis on one of the string.

English construction is often confusing, as are the plethora of words with different meanings spelled the same way, such as lie, meaning an untruth, or lie, meaning to lie down. But some English rules need to be observed for the sake of clarity-not to mention sanity. For a really good grammar website, visit the Guide to Grammar and Writing.