The above is really, really very good advice. Certainly true about not getting disheartened by bad marks etc. I wasted marks here and there in year 11 because of my bad time management and started kicking myself, knowing I could have done much better if I had been working on the assessment from the day I got it, or using the holidays to study more and so on. However, this got me much more motivated for year 12. You can, and should, put in a decent effort for year 11, but remember to look back once you've finished and think, 'Well, that was just the practice run.' Identify where you went wrong and WRITE IT DOWN, then figure out how you will avoid it in year 12.
And on top of everything, WRITE DOWN YOUR GOALS. Write down what you really want to achieve. Many people don't do this because they are afraid of aiming to high and failing to reach those goals - this is one of the worst mistakes you could make. When you have clear, definite goals to strive for that are high but still realistic, then you will be ever so much more directed in your approach to learning. People without goals tend to 'wander' aimlessly - its a sorry sight to see when you know just how much more they could be achieving.
Sorry this is a bit jumbled, but just a bit of advice - hope it helps! good luck to you all - todays achievers are tomorrows leaders!