I struggled with this a lot too and it ended with me scrapping a few projects because the main character wasn’t strong enough. I took it to the next level though, in that my character wasn’t just me, she was a perfect version of me. It was to the point where I inserted into her so much of myself and who I wanted to be that she made all the characters around her look like buffoons in comparison. It doesn’t sound like you’re doing that though so that’s good!
I’m by no means a master writer but I’ll share with you what helps me with characterization.
First, I think it’s important to clarify that your characters will probably reflect you in some sort of way. In fact, many well-published authors claim that this is the best way to make characters: tear off a piece of yourself and give it a name. While not everyone can relate to every aspect of your personality, I guarantee there are parts of you that people will relate to. If your character ends up having a lot of insecurities like you, well guess what? Lots of people have insecurities! You’re much more likely to appeal to a large audience if your character has insecurities than if your character is completely happy with every aspect of themselves. So embrace the parts of you that you see in your character because it only makes them seem more real.
Now onto what helps me. One of my favorite aspects of writing and characterization is dialogue. I love inserting myself into characters’ minds and deciding how they would speak, or what they would say in this situation to this other character, etc. I think dialogue is one of the funnest parts of the writing process because you can learn so much about someone by what they say. I also use dialogue as inspiration for many of my characters’ personalities.
I have a whole board on my Pinterest of dialogue prompts that I find fun and inspirational. In fact, the first interaction between the two MCs in one of my WIPs was taken from a dialogue prompt that I found on Pinterest. The interaction is two lines long and yet it set up not only their personalities but their relationship as well.
“Oh, good,” [name_m]Zac[/name_m] said, not looking up. “You’re still alive.”
I threw my hat onto the table. “[name_m]Don[/name_m]’t sound so disappointed. I might start to think you don’t like me.”
Of course, the dialogue prompt didn’t have tags or other motion surrounding it, but I knew after reading it that it was perfect for these characters. It has playful insults, suggesting that the two of them are probably close, and are also the types to roast their close friends. [name_m]Zac[/name_m]’s tone is nonchalant when he says that [name_f]Petra[/name_f] (the narrator) is still alive, suggesting that she often does things that put herself and her life in danger, maybe indicating a lack of impulse control (spoiler alert: she’s extremely impulsive). Finally, [name_f]Petra[/name_f]’s first instinct was to say something snarky and sarcastic in response, which suggests a certain amount of confidence, as well as showing that she has an attitude. A lot of characterization in only 2 lines of dialogue, and it helped set up the personalities of these characters for me. So, while I’m not really an impulsive person myself, I’m in the mind of someone who is, which helps me write her character in that way.
I’m not sure if this will be your fix as I understand writing is the furthest thing from a one-size-fits-all ordeal but my advice is to take some time looking at dialogue prompts. I’m not sure what social media you use but Pinterest is my favorite place to find them. I’ve also seen a lot on Instagram (and those were often taken from Tumblr so I can assume there’s a lot on there). The Fake Redhead‘s dialogue prompts are my favorites. I recommend not having a character in mind when you’re looking at them and just wait for one to speak to you (no pun intended). If you have a voice, you have a thought process, which is a large part of personality.
Good luck!