Common Edits - Farther, More Than, Each Other

The rules for farther/further, over/more than, and each other/one another are pretty clear, and if you get them memorized, you should be able to apply them correctly with ease. (My example sentences aren't great writing; I'd suggest edits for each of them! But we're just hamming it up to highlight differences.)

Farther/Further

Deciding when to use "farther," ask yourself if you're going an actual, measurable physical distance. How FAR is it going? FARther. 

And if it helps with when to use further, think of FUR, how it's something growing out from deep within, like an internal to external, and let's have it represent abstract measure. Use further to mean in-depth, abstract, thought/feeling-dimension movement; to a greater degree; in addition. Warm and furry thoughts and feelings and the like.

• Let's further discuss this farther down the road.
• Don't let the evil seep any further in your heart.
• My father didn't let me walk farther than the front door before he further drilled in the consequences if I missed curfew.

Over/More Than

Basically you're going to use "over" for anything except when it's countable, when it's a "greater than" situation. "Over" will include abstract concepts and not just physical movement--but of course not exclusively. Hopefully it will feel intuitive which to use when, but if both sound okay and you're talking countable objects or subjects, I'll likely edit "over" to "more than" in those instances. If it's in dialogue and that's how it sounds when someone/your character speaks, we don't have to edit to adhere to grammar rules. Correct verbiage can sound worse than common usage.

• I'm over the moon that we found more than three moons orbiting that planet.
• I have more than thirteen years of editing experience.
• I'm more than happy to help you get over your illness that you've suffered more than five times over the past month.
• We haven't had you over in more than a year!
• She's over seventeen, so she gets more than seventeen kisses. (Age is abstract number vs countable number of kisses.)
• Don't go over twenty minutes, okay? (What we're not saying here is "don't go over [the time limit I'm giving you]"; so even though "minutes" are countable, the abstract use of time is our focus, not the actual minutes.) You could also say, "Don't let more than twenty minutes pass after eating before you take your pill," and there you're focused on the numbered minutes indeed, so you'd use the "greater than" meaning of "more than."
  

Each Other/One Another

There's a difference to these? Sure! But it's not extremely important in most cases. Simply put, "each other" is used when it's two entities interacting, and "one another" is correct when more than two are involved. I think of "I've got one in each hand, so I have two" as my memory device. This "rule" is very much another case of "my character wouldn't say it that way" so we then don't force grammatical accuracy and leave it be.

• As I have loved you, love one another.
• The delegates from each country couldn't agree with one another.
• I know we thought they'd make a good match, but it seems like they can't stand each other.
• The survivors hadn't spoken with one another since the incident where the ships crashed into each other.

If this helps you, happy day! Hopefully a quick and clarifying lesson. As ever, focus on your story craft. Do your best, don't let Grammarly lead you blind (the unnecessary second-guessing it forces upon you will stress you out more than it's worth), and I'll see to the rest.