Most people are going to be playing characters that are a little more down to earth, though there are some out there that take rule of cool perhaps a little too far than what’s generally accepted. Under no circumstances are you obligated to RP with a person if you do not wish to, so if someone’s taking their RP too far you’re free to ignore them and carry on.
If you’re new to RP, this link is a great resource for getting started: [Guide] Roleplaying FAQ
Otherwise, I would say keep your first idea simple starting out and worry about fleshing out finer details later. This doesn’t mean you have to start out as a dirt farmer or anything; rather, focus instead on what general role the character fills in society and what their personality is. Then get a loose idea of how they got there and what their general goal is moving forward. Doing that will give you a good starting base to build on. Don’t be afraid to modify details as needed either–oftentimes, RPing the character will give you better ideas on who they are and where they’re going/what they want.