Note that these are based on discussions I've had with other writers and on various blogs and craft books I've read as well, but in the end, they're my own opinions.
Active Versus passive voice.
Most of us were told at one time or another not to use passive voice in our writing, but many people are unsure of what passive voice is.
Some people think that any use of a "to be" verb in a sentence is passive, but this is not true. Passive voice is when the subject of a sentence is the recipient of its action. So in the above sentence "most of us were told at one time..." is passive voice, because most of us (the sentence's subject) is being acted on by its verb (told). The second part of the sentence "but many people are unsure..." is not passive, because the sentence's subject is performing the action. "Many people" is the subject, and they're performing the action of being unsure.
It's really more accurate to think of clauses within sentences as being active or passive, rather than the sentence itself, because complex sentences can have multiple clauses. Consider the following sentence:
"I went to the fair and was approached by numerous people while I was there."
The first part (I went to the fair) is active, while the second part (was approached by...") is passive.
You can also have a passive clause with no to be verb: "Racked by stomach cramps, I raced to the bathroom."
The first part of this sentence (Racked by nausea) is passive.
While the overuse of passive voice can indeed make writing cumbersome and roundabout, it has a place. For instance, rewording the sentence "Most of us were told at one time or another not to use passive voice..." requires us to actually state who did the telling so we can turn them into the subject of the sentence.
Our teachers told most of us not to use passive voice..."
This works well enough if we want the focus of the sentence to be on teachers, but if we want the recipient of the action to be the focus of the sentence, then keeping it passive is appropriate.
Like anything else, use it mindfully and for a reason.
How long should my chapters be, and should they all be the same length? This one comes up a lot on writer's groups. The best way to answer this is to grab some novels down from your overflowing bookshelves (if you're interested in writing fiction, I'm assuming you're also a bookworm) and see for yourself.
The answer, of course, is that answers can vary in length from a single sentence to tens of thousands of words. The average length of chapters in a book will depend on the pacing, the structure of the story, and personal preference. Some writers (Pratchett is one) don't use standard chapter breaks at all. And many writers vary chapter length quite a lot within a given novel. Typical adult novel chapters are between 2000-5000 words long, but some are longer, and some are shorter. Use the approach that works best for your story.
Describing a character when you're writing in limited third or first person.
This one comes up a lot. Obviously, you can't randomly zoom the camera out when writing in character pov, and mirror scenes tend to be clichéd. So how do you show the reader how your character looks if you don't want him or her to come off as incredibly vain or self conscious?
The first question to ask yourself is how much detail does the reader need? Is the precise color of your protagonist's eyes or the precise shape of his or her nose important? Most readers are pretty good at drawing a decent mental picture from a few generalities. There are some details of appearance that can be important, however. Maybe your character has some feature that makes him or her stand out or that makes other people react to him or her in a certain way. Say your character has a hideous scar, or is of a different race than most of the people around him or her (sadly, most readers will assume a character is white, unless shown otherwise).
In these cases, it might be plausible to show other people reacting to the character's appearance and possibly to have the person thinking about his or her appearance. For instance, someone calls your protag "Ginger," or asks him how the weather is up there, or stares at the scar on her face. Another technique is to have the character responding to the appearance of another person. In the beginning of Jay Lake's novel Green, the protagonist is seeing a white man for the first time, and her reaction to his appearance leaves little doubt that darker skin, hair and eyes are normal to her.
Inciting/initiating event versus plot catalyst
This is one of those pesky terminology questions, because different writers and editors will use different terminology for the same concepts. Typical stories have something that gets the ball rolling at the very beginning of (usually by the end of the first chapter). It is sometimes called the inciting event or initiating event or first plot point. This represents a break in business as usual that nudges the story along. In character-driven stories, it's most often something that happens to the character directly, but sometimes it can be something that happens off camera, or in a prologue. Regardless, it will disrupt the life of the main character or characters.
Stories that feel like they have ridiculously slow starts often are so because the inciting event happens too late.
The plot catalyst typically happens later on in the story (10-15% in usually), but still in what can be considered the first "act." It can be an event, another character, conflict etc. that forces the protagonist to make a choice about whether to act in some way. It's sometimes called the point of no return, because once it happens, there's no way out for the main character(s) but through.
Stories where it feels like the protagonist is wandering aimlessly for too long are often missing this element.
Is it all right to write characters who are a different gender, race, sexual orientation or culture than myself?
Yes. If it weren't, then many classic works of literature would never have been written. If you're writing something about or from the point of view of a culture or life experience you're not very familiar with, however, it's probably a good idea to do your homework, and to spend some time learning about stereotypes and potential pitfalls. Research what cultural (mis)appropriation is and how to write about other cultures, or create new ones that integrate aspects of existing cultures, without doing this. And run it by a reader or two who can tell you if you've made any gaffes.
And most of all, be aware that everyone is first and foremost an individual. No character can be a generic representation of his or her gender, orientation or culture, anymore than you yourself are.
But aren't you supposed to write what you know?
Write what you know is probably the most mis-cited, misunderstood piece of writing advice in existence. If writers could only use settings, experiences and characters that they have lived directly, or about which they are experts, most novels would never be written.
Write what you know means you are supposed to bring your own lived experiences to the table in your writing on order to create believable and emotionally authentic responses, but it doesn't mean that every character must be (or should be) you, or that you must have personally done everything your characters have. Use your capacity for imagination and empathy, not to mention your experiences with different people and situations, to create realistic, three dimensional characters.
And be willing to research things too. Never been in a battle? Don't just study historical records of real battles (though this is a good start). Read first person accounts of people who have.
This is a good breaking point for this week, but I've got plenty more FAQs that come up on writing forums and in workshops.