The two most important aspects I look for in an adventurer's background are the following:

• What caused them to leave their friends, family, town, occupation, etc to start adventuring? (This could be because of wanderlust, leaving a bad situation, seeking something/someone, pursuing a goal, etc)
• What caused them to seek a group (aka 'party') to adventure with and what is their motivation to be a good party player? (This could be because they are an affable type, want to overcome an obstacle larger than themselves, because they are duty bound, etc)

I find that these two items can help you and your character relate to other players' characters and provides broader opportunities for the GM to weave your backstory into current narrative (if they so choose).

A character backstory also does not need to be fully inclusive. You shouldn't need to run down a checklist or create an online dating (or dwarf fortress) profile. Your character can be allowed to like apples or have a morbid sense of humor but those things may not be important enough to codify in a backstory. Being more generic instead of super specific can also help the GM in tying your background into the plot (especially with relations and places). Saying "I grew up with two siblings in a small town" gives the GM more creative freedom than saying "I grew up in Placetown with my butcher brother Bob and soap-maker sister Sally."

Your backstory does not have to be a constant, set-in-stone document that is fully defined from the beginning. Your character can (and should) evolve as time goes on.

Lastly, don't hype yourself up too much. If you're a level 1 PC you probably haven't done too much yet. At this point, you're an unknown moisture-farmer kid on some backwater dust-ball planet. You might be ready for greatness, but you haven't yet had opportunity to act yet.