The word data is plural. The singular form is datum. The data are… The datum is… While correct, I’ll admit it does feel weird to say. My recommendation is to charge your sentences that involve these words to remove the is/are or was/were. The data shows…
It’s a common mistake made, and one I often have to look up, just to reaffirm what I already know. Affect is the verb, where effect is the noun. It doesn’t help the confusion when the word “influence” can be used to replace both words.
It’s Achilles’ heel but James’s foot. Only ancient names that end with an s do not employ a possessive form of ‘s. All modern names do. One way to avoid the confusion is to rearrange the wording: the heel of Achilles but the foot of James. Yes, it adds words, and sounds a little stuffy, but the confusion of the possessive form is gone. (Note: While not all style guides agree, most do.)
Whenever using acronyms in writing, non-fiction or fiction, one needs to define what they mean—normally. In fictional writing, if you mention the FBI, most will accept that this stands for the Federal Bureau of Investigation. But that SIFFY… No one will guess that it stands for So It’s Fast and Furious Youth.
Phrases like “sit down” and “stood up” have redundancy built in. Down is the only direction one can sit (unless you’re in space) and there is no other way to stand except up. However, Jill can sit next to Jack, but she’s more likely to tumble after him.
The word gray, or grey, is one word where both forms are accepted by both a US and UK English spellchecker. So which is it? An easy way to remember: GrAy is for American English, and GrEy is for English English. There will be places that will prefer one form over the other. However, if in doubt, that simple rule will help.
Let punctuation do some of the work for you in dialogue. “Help me,” she shouted. Instead of a dialogue tag, just use an exclamation point. “Help me!” The same can be said for asked and the question mark. “How can I help?”
Some subscribe to the theory that you should never use adverbs, but they do have their place. Sometimes they add that something more. Let’s face it, a spindly branch is better than saying thin branch.
All of us need to breathe, and our characters should be the same. However, be careful with the repetitive use of those actions: taking a deep breath, sighing, remembering to breathe. Search for them, and ensure that you haven’t overused them.