You've probably heard the famous quote from Stephen King: "The road to hell is paved with adverbs." It's true, adverbs are rarely necessary in writing. But when it comes to character development, adjectives, when used too simplistically, can be your downfall, eliminating your ability to create well-rounded, unexpected, genuine characters. Adjectives, along with cookie-cutter formulas and never-ending character development questionnaires (no one cares what your character's favorite ice cream flavor is) can further complicate the already difficult task of creating great characters.
All writers have their strengths and weaknesses. We improve ourselves as writers when we embrace the elements we're not as skilled at, and work to figure out a way to make them work for us. And when it comes to character development, I often find that writers have severe preferences, relying on only one method of characterization. This creates predictable, unoriginal characters that won't stand up to the scrutiny of publishing.
So what's your developmental rut? Do you rely too heavily on physical habits? Perhaps your character smirks at every comment made to him, or giggles before every other line of dialogue. Are you caught in the trap of insinuating character traits based on physical description? Your red-headed character doesn't have to have a fiery attitude, and your bald guy doesn't have to be tough. Patterns like these are easy to fall into and end up diluting your characters. We need basic description sometimes, yes, but more importantly, we need multiple ways in which to discover new things about your character.
So how can you ease the road and ensure more compelling characters? Invest in them! How do you make good investments? Diversify! If you think of it like an investment strategy and actively diversify the ways in which your characters are presented, you can smooth out your characterization into a more balanced and seamless portrayal. Just like you wouldn't want to put all your money in the same company's stock, you don't want to use only one method of developing and portraying your characters. Branch out from your ingrained developmental habits and try working some (or all) of these ideas into your project, rather than grounding yourself on the same developmental sandbars.
Voice and Dialogue:
This one makes the top of the list because it's the most important. Your characters must sound different from each other. Not only that, but they must sound different from you, the author or narrator. A character's voice does not refer to whether they sound nasally or high-pitched or raspy. A character's voice is the way they phrase things, and is often a neglected aspect of development.
Listen to the people around you in your everyday life, and pay attention to the way they speak. You can take inspiration from their idiosyncrasies and use them to help your characters find an individualistic voice. Keep in mind that "individualistic" should never turn into "cliche" or overly affected. If your character from England is overly formal when compared to everyone else, you might have a problem. If your teenage girl says a lot of air-headed things, or says "like" in every sentence, you might have a problem. Think deeper. For instance, I have a friend who loves to use examples to explain things, and she uses her hands to draw "illustrations" in the air as she talks. My mother often will get distracted in the middle of a sentence, but always comes back around to what she was originally saying. It's these kinds of more complex speech mannerisms can make the difference between flat and compelling character dialogue.
Not sure if your characters all sound the same? Here's a good test: Take a section of dialogue from your manuscript and erase everything except for the words within the quotations. Strip it down to nothing but the dialogue itself. Then, ask someone to read your sample and tell you how many characters are involved in the conversation. If your characters have solid, individual voices, your reader will be able to pick up on them.
This particular category of characterization is more complicated than most writers assume. It can encompass both a description of physical characteristics, or the physical actions of a person, such as ticks, gestures, habits, facial expressions, etc.
Describing the physical appearance of your character truly has little to do with good character development, unless it's necessary to the story. Describing a character's hair color, eye color, clothing, or build won't get you very far. You can make them look like whatever you want, but I don't honestly care if they have two different colored eyes or a roguish smile - these kinds of things are often attempts at manufacturing interest where there is none. However, if your character has a tattoo of a past significant other who appears later in the story, that could be justified as a more concrete development. If your character has a particular physical ailment or scar that can be attributed to another event or person in your story, that could be justified as a more concrete development. If your character is tense, or fidgety, or chews with his mouth open, you should make every effort to have a connective tissue behind these things. Don't make him apathetic or aloof just to make him appear cool - we need more substance than that.
Not every piece of your character needs to be nailed down and attached to his backstory, but being mindful of flimsy or arbitrary attributes will strengthen your characters. Be honest about yourself whether a developmental element is too surface-level, and if it is, are you leaning on it too much for development?
Choices say a lot about a person, as well as how one comes to a decision and the way they examine their options. So you can use your story's conflict to push boundaries with character development. By writing difficult or interesting circumstances into your story, you force your character to define him or herself by taking action. It's ok to make life difficult for your characters, and it's ok not to give them all the tools they need to act appropriately. In fact, I encourage it! If there's a hole in your character's boat, get rid of any easy way out. He doesn't get chewing gum to seal the hole, he doesn't get a kind passerby to assist him, and he doesn't get a calm summer day in which this occurs. Make him drop his wallet into the lake, make him lose his only oar, and make the water 55 degrees F. Force your characters to make choices that are difficult and defining. In doing this, you'll not only give them the opportunity to prove who they are to the reader, but you'll also kill two birds with one stone by ramping up the conflict of your story (a lack of which is another common issue).
I also highly encourage having different characters in your cast make opposing decisions. I often see manuscripts in which everyone agrees with each other all the time, which makes little room for any kind of interest. Brothers don't always have to work together, couples don't always have to make up, and everyone doesn't have to be on the same page. In diversifying the decisions and opinions your characters have, you successfully introduce diversity of thought into your cast and give yourself many more creative options to pull from. Character writing is essentially a form of acting, so get into your character's head and figure out what they would truly do in their situation.
These are just a few different ways to really enhance your characters and breathe life into them, and there are many others. Diversify your methods, and describe your character from more angles and in different lights. Mix and match, and decide which methods would best highlight the pieces of your character you want to bring forward. Think harder. Differentiate and complicate. No one ever said you have to use a certain formula for character development, so think freely and unlock more complex individuals by deviating from your favored process.