The MAIN character is the MAIN (get it?) thing you need to focus on before writing a book. They must be realistic (unless a sociopath or a psychopath) and have to have a personality that the reader can somewhat relate to. What I do is write parts of myself into the main character, in my book 'Life As He Knows It' I based the character (Ben Snow) off of myself; meaning he has my thoughts and feelings. But if you're a little weird (like me) and want what people call a 'normal' character, I suggest that you take some time to stalk people. DO NOT be creepy while doing this.
If you want a strong female character, I suggest that you read books and watch movies with strong female characters in them (not 'Twilight'). Examples: 'The Hunger Games', 'Paper Towns', and 'The True Lives of the Fabulous Killjoys'. Strong female characters don't HAVE to be main characters in other things. Stay away from classic vampire/werewolf novels.
If you are seeking a more mellow MC, I suggest that you spend some time at the beach and look at the waves. Think about how nice and calm it feels to be there, and not about writing at all. The best way to write a novel is to not think about writing a novel, just so you know. Walk through a field of flowers and think about how good the ground feels against you bare feet. It's nice to get away from loud people for an hour or two, yes?
this is where i ramble; have fun