I want to talk about some tips for streamlining your writing and giving it more impact (as well as making it more "correct," grammatically). These tips address problems that even competent writers have. I catch myself making some of these mistakes. But afterward, I always discipline myself appropriately, for example by withholding extra servings of gruel.
Subject-pronoun agreement is a problem for many native speakers of English. I'm not sure why. It's easy enough to avoid. An example of what not to do: "When you ask a person to help you, they will often refuse." Why is this wrong? The pronoun "they" is a plural form, yet here it refers to a singular "person." It's correct to say: "When you ask a person to help you, he or she will often refuse." Or, if you prefer the plural: "When you ask people to help you, they will often refuse." Do one or the other. Don't mix "they" or "them" with a singular subject.
Avoid the word "very." Instead, use a higher-impact (and/or more descriptive) word like "extremely," "exceedingly," "hugely," "remarkably," "astoundingly," "astonishingly," "massively," etc. The word "very" is overused and thus has little impact. It's supposed to magnify the impact of whatever it's modifying, but you can't increase the impact of something by modifying it with a low-impact word. So just avoid "very" altogether. Think up something more imaginative. Imaginative words improve almost anybody's writing.
Eliminate unnecessary uses of "that." "He knew that it was wrong" can be improved by saying "He knew it was wrong." This may not sound like such a big deal, but if you use "that" needlessly throughout a lengthy piece of writing, you'll find it tends to bog things down. If you're looking for a super-easy way to streamline your writing, start by finding and removing unnecessary thats.
Stay away from "There is...that" constructions. Don't do this: "There are many cars that aren't reliable." Instead say: "Many cars aren't reliable." Why would you want to use seven words to say something that can be said in four words?
Don't put an "-ing" word at the start of a sentence, unless you really know what you're doing. In English, an "-ing" word is (grammatically speaking) either a present participle or a gerund. The difference between a participle and a gerund is that a participle is a verb form used as an adjective, whereas a gerund is an "-ing" verb that serves as a noun. Either way, the brain rebels. Your brain doesn't want to see verbs used as adjectives (nor as nouns). So avoid "-ing" verbs wherever you can. Sometimes you can't avoid them, of course. "Revolving door" uses the participle "revolving" to modify "door," which is fine; the meaning is clear. "Interrupting is rude" uses the gerund "interrupting" as the subject of the sentence. Not bad; it's short, and the brain can parse it okay. But consider: "Paying attention to grammar eliminates mistakes." That's a poor sentence (what's the subject?), as is "Being thin avoids heart disease later in life." Stay with nouns as the subjects of sentences and you'll find that sentences are easier to write, as well as easier for the reader to understand.
Be careful about decoupling the object of a sentence from the predicate. Example of what not to do: "Throw the horse over the fence some hay." The subject of this sentence is an implied "you," the object is "hay," and the predicate is "throw." But that's not how the sentence reads. It reads as if "horse" is the object, which is wrong. Presumably, you want to throw hay, not a horse, over the fence. If you were to say "Throw hay to the horse over the fence," that's still not good, because you're implying that the horse is over the fence rather than that you need to throw hay over the fence. If you actually want somebody to throw hay over the fence, say so: "Throw hay over the fence, to [or for] the horse."
Don't let ambiguity creep into your writing. "The ability to read quickly made him smarter." Does "quickly" modify "made" (quickly made)? Or does it modify "read" (read quickly)? It's ambiguous. Completely reword the sentence if necessary. Try something like "He became smarter because of his ability to read quickly," or (if "quickly" applies to "made") "He quickly became smarter because of his ability to read." Say things in the most unambiguous way possible, even if it means making sentences longer.
And by the way: Much of the time, you can ignore the old rule about not allowing a sentence to end with a preposition. Examples: "That's a subject I know nothing about." "It's nothing to cry over." "That's what the dog sat on." "Do it that way, if you have to." No one but the most pedantic schoolmarm would consider such sentences wrong.
Tomorrow, I want to talk about certain words and usages that cause trouble (yet are easily made right). The words in question are like land-mines waiting to blow big craters in your writing. Ignore them at your own peril.