Let’s talk about the different kinds of autobiographical characters one can create. There’s a whole spectrum between ciphers and wish-fulfillment Mary Sues/Gary Stus.
1. The thinly-fictionalised version of yourself. Seriously, why even bother presenting your real-life story as if it were a novel? Just write a memoir or publish your old journals and be done with it! Bully for you that you had an idyllic childhood with no major problems. You might write these stories beautifully, but even a deliberately episodic, slower-paced, character-driven book or series where coming of age IS the plot needs hung on some kind of trajectory and story arc.
Give us tension and stakes, not just a bunch of random episodes or silly, minor dramas that easily, quickly resolve. If you’re drawing solely from your own life, or only slightly tweaking it, odds are you won’t have the kinds of plots and characters that drive along a good yarn.
A lot of these autobiographical or thinly-fictionalised stories also are only interesting if you know the people involved. E.g., you’re charmed by stories of your grandparents playing paper dolls and eating lunch in a piano box, but could care less when anyone else does it. At least use it to further character development or elevate it beyond a random episode.
2. The wish-fulfillment Mary Sue or Gary Stu. This is the kind of character who gets all the job promotions, successful art shows, military advancements, high grades, spicy sex life, etc., which you never had but always wished for. No one wants to read about a perfect character with a charmed life.
3. The bully pulpit for your frustrated failed ambitions. It’s so obvious when a writer uses an autobiographical character, or one with a similar life trajectory, as a way to constantly whine about why s/he didn’t get those military promotions, salary raises, successful art or music career, scholarship, dream job, etc., or to blame it on everyone and everything but oneself.
Maybe it really is unfair how you lost or were never offered those opportunities, like spiteful co-workers, a boss who inexplicably hated you from the jump, or the kids from well-connected families being ushered into your school’s college prep track despite not having very good grades. You can explore that with a story based on your own life, but dwelling on it and ranting so often makes you look unhealthily stuck in the past.
4. A character based strongly on yourself, but with some significant differences. I’ve spoken many times about how Emeline Troy is my Doppelgänger. We both had hyperlexia at age three; the first book we ever read was the adult, uncensored Grimms’ Fairytales; we adore Hermann Hesse; we’re very influenced by Eastern philosophies and religions; we didn’t have our first relationship till age 28; our beaux were both walking DSMs from emotionally incestuous immigrant families, maintaining a hurtful, inappropriate friendship with a deranged ex, and with a bizarre aversion to kissing; we both had menarche a month before our twelfth birthdays; and so much more.
However, I only wish I’d gone to Vassar; I didn’t have a double major in history and German Studies; I didn’t switch to a private school for disadvantaged young women, on full scholarship, late in my sophomore year of high school; I was cheated out of the chance to study Latin my last two years of high school; I don’t have eight siblings; my walking DSM ex is Belarusian, not Hungarian; I didn’t grow up in tenements or in NYC; and I’ve never smoked pot.
5. A character based somewhat on yourself, but fully her/his own person. E.g., this character might have a different religion, ethnic background, political party, or hometown than you, but have a similar family background, personal values, and hobbies. There are also a number of incidents drawn from or based on your own life, but not to the point of a strongly autobiographical story.
6. A character who lets you vicariously explore the path not taken. Maybe you’ve always regretted a certain choice and wished you’d made a different one, or always wondered how your life might’ve turned out had another opportunity been available. E.g., taking school more seriously and qualifying for a full scholarship to a prestigious college, accepting a job offer in another country or state, marrying and having kids earlier or later, getting financial aid for a private school with an excellent music program, studying abroad, not being so provincial, studying architecture instead of business.