I'm definitely not the best writer in the world.  There are scores of writers that write so much better than I do.  But there are some mistakes they make that I think I have been able to avoid, and avoiding them is actually easy.  They mostly have to do with words that either sound similar, or a word choice that seems reasonable, but is just slightly wrong.  I'm not infallible, but this post is a starting point; if I don't do anything else that's useful for my fellow-writers, at least I can die happy that I did this.

Words that sound the same, but mean different things

Peddling, pedalling.  Pedalling is driving a bicycle with your feet.  (She looked over the wall, and saw Jill pedalling down the street as fast as she could.)  Peddling is selling.  (Jill wondered what the guy was peddling now.)

Peaking, peeking, peeping.  Also piqueing.  Peaking means to have reached the very top of your skill.  (Jill's speed had peaked; it was downhill from here on.)  Peeking is to spy on a scene from in hiding.  (Jill peeked on Santa, sneaking the cookies.)  Brits and Commonwealth folk---and occasionally someone from the Northeast---use the word peeping instead.  To pique is to grab the interest.  (Jill's interest was piqued by the colorful book cover.)

Moose, mousse.  Moose is a big critter, like Bullwinkle.  Mousse is stuff that some people put in their hair, to make it lie flat.

Past, passed.  The past is an earlier time.  (My gradmother dwells in the past.)  Passed is a verb, signifying that you've overtaken something, or succeeded in a test.  (The paper was so good, Jill passed the course.)

Queue, cue.  A queue is a checkout line, e.g. at a grocery store.  A cue is a signal for something to take place.  ("That's your cue to leave.")

Pouring, poring.  Pouring is to spill a liquid out of a container.  To pore is a rare usage; it means to study a book closely, looking for something.  (Jill pored through the agreement, looking for problems.)

Lead, led.  This is tricky.  Lead is a soft, gray metal.  Stainglass windows have the colored glass separated by lead.  To lead a group means to take the guiding position.  If someone has been a leader in the past, we say that she has led a group.  Led is simply the past tense of the word lead.  There is a word called leaded, which has nothing to do with the verb lead.  It is the word for glass that contains the metal lead, or paint that contains lead salts, or stainglass windows.

Come, cum.  Come is simply to come towards somebody or something.  Cum is a relatively uncommon Latin word that means also.  (Jill was a housekeeper-cum-nanny.)  I pronounce the word cum as "coom", but that may not be a universal thing.  Catholics familiar with the Latin liturgy might recognize the phrase cum Sancto Spirito, which means [who,] together with the Holy Spirit ...

Pedals, petals.  Pedals are the gadgets that you press with your feet, e.g. the accelerator / gas pedal in a car.  Petals are the cute little things that are in a flower.  These words should not be pronounced the same way, but unfortunately many people do.

Discreetly, Discretely.  Discreetly is an adverb, meaning to do something quietly, or without causing alarm or offense; or attracting too much attention.  Discretely means separately, a word that has more technical usages than colloquial ones.

Leant, lent, Lent.  Leant is the same as leaned, the past tense of lean.  Lent is the past tense of lend.  (Jill, I need back the hammer I lent you.)  Lent is also a season of the Christian calendar, lying between Ash Wednesday and Maundy Thursday.

Gate, gait.  A gate is essentially a large door, perhaps in a fence or garden wall.  A gait is a manner of walking.  Most people have an fixed way of walking; and someone watching from a distance can often recognize a person from their gait, even if their faces can't be seen.  Horses have many gaits, a trot, a gallop, are all different gaits.

The next several items are just words with usages that some people get wrong.

Social, Sociable.  The word social simply means: having to do with society.  In some places, it means a party.  Sociable is a word used to describe someone who likes to get together with others, and has lots of friends.  (Jill is a reclusive girl, but Jack has lots of friends, and is a sociable fellow.)

Bare back, bareback.  Bare back refers to someone's back, without a covering.  To ride a horse Bareback means to ride a horse without a saddle.

Easygoing, easy going.  Easygoing describes someone who is relaxed, and not particular about things.  Easy going means some task that doesn't give you problems.

If, whether.  The word if is a word of logic: if you like horror movies, stay with us!  But some people use the word if to indicate uncertaintly:  I don't know if you like horror movies!  The more conventional word to use is whether.  "I don't know whether you like horror movies!"

Everyday, every day.  Everyday means ordinary.  "Oh dear, I wore everyday clothes; I didn't know it was an occasion!"  Every day simply means each day.

Hangout, hang out.  Hangout is a place.  To hang out is to spend time with someone.

Creep, crept.  Crept is the past tense of Creep.

Kneeled, knelt.  Knelt, and kneeled are both past tenses of kneel, but they have slightly different usages.  Still, I think using them interchangeably is not really unforgiveable!

Sat, seated.  I just notice the use of the word sat to mean seated, by British writers.  (Jill was seated right across from Jack.)  Let's be clear; any wrong usage will eventually be accepted.  The grammatical universe is heading in the direction of not caring too much for correct usage.  But if clarity and understandability are your goals, it makes sense to tweak your writing a little bit, so that it is not confusing, even if you sacrifice a few colloquialisms that are dear to your heart!

This a work in progress is.  If I have the energy, I want to order then entries alphabetically, and maybe group things in some way.

Hope this is useful!  --Kay