As a player, I write long detailed backstories and revel in them. Then I’m put in a group of strange characters and I have to somehow bring that backstory to life, while simultaneously battling enemies, making deals, and trying not to die. It’s difficult to decide how exactly to portray backstory. It’s important to have that backstory for yourself, but a lot of backstories are really cool — we want people to know the tortured details of our past, and how they relate to our motivations. Everyone has a story, and, done well, that story can unfold over the course of the campaign in a way that is satisfying for everyone.
The most important thing is not to let your backstory get in the way of your role playing. I have seen characters before whose backstory was so tragic that they couldn’t look at people, or never spoke, or refused to go outside. Or they have such a deep dark secret that they never get close to anyone or leave a room or situation when the conversation turns personal. That sort of character trait is cool and melodramatic in theory, but in practice, it prevents other people from interacting with you, and gets on their nerves. Good role playing is about give and take–if your character refuses to engage, neither you nor your party members are going to get anything out of it. You can still be reluctant to engage, but you have to allow yourself to be drawn out to some degree.
If you have a dark secret, expect it to come out at some point. Take it one step further–PLAN on it. Having a dark secret that haunts you, or a twist in your goals that the party doesn’t know about, or something you are on the run