

Get flubber.

Find a good district club with strong coaches. Listen to them, do extra/individual sessions if you can to work on your general skills, shooting and fitness. Serve your team first and work hard.
Worry less about what you can't control (your height, for example, maybe athletic ability) and worry about what you can control - dedication, skills, etc.
Read this blog entry by Isaac White on Andrew Jantke's site: Mental toughness and dedication. It's really impressive.
Not everyone has the follow-through to work that hard, but set yourself tangible goals and work at them. A lot of things that are useful in basketball no doubt apply to other lines of work and life in general, so effort in those areas won't be wasted.
There are a number of examples of undersized or unflashy players who had reasonable NBL careers. In the event that you are not an outlying talent by default, that calibre of player is probably not beyond a generally fit and remotely tall player. If you're not projected to be 6'+, then playing ABL on the side of another career is not out of the question.
Always have a back-up plan though. At NBL level, anything other than the top tier is going to one day retire and probably need a backup plan unless they've invested well.
Focus on your short term goals. They will be stepping stones on the way to your distant goal. They will be the things you do this year - shooting, fitness, etc. Ask your coaches for feedback. If they're scrub coaches in a lower division, also see if they can help you get feedback from the div one coaches in your age bracket and the bracket above. Coaches of almost every level will be happy to give feedback to a dedicated and genuine upstart. Once you're a bit older, NBL players will be able to give you practical feedback too - almost all the ones I've met have been decent, genuine sorts.
Disclaimer: I never played basketball beyond social/community level, but I've watched my brother's career closely, plus those of his district, AIS and NBL peers, and have a lot of respect for some of the really solid, dedicated coaches I've interacted with locally.

Be 6'6 or taller.
Have a wing span of at least 7'.
Have a 38 inch or higher vertical leap.
Work on your ball handling no matter your height.
Work on your outside shooting no matter your height.
Work on your finishing no matter your height.
But more importantly - watch film. Lots of it. Watch documentaries and highlights and full games of the best players.
Mimic their moves, study how they see the game. Incorporate their thinking into your play.
Don't be selfish, make others better, but be the man when you team needs it.
Most importantly have fun, at only 11 if you go to seriously, you'll be burnt out by 16.
Find a coach that will nurture your skills and not just use you because you might be tall for your age.
