Hi
You need to focus on both your academic subjects AND extra curriculum stuff too. he academic training to become a lawyer is not difficult if you focused, getting a training contract is the hard part. For every 20 graduates there is 1 training contract, so you need to set yourself apart from other lawyers to be.
Try to get some work experience in the holidays, apply to local small law firms ( at 14-15 you wont get any big firms offering work experience) and ask to work for free, even making cups of tea, or running errands.
If you don't have a Saturday job try to get one. Your CV will look good if you can show you have worked hard to support yourself from a young age.
If you are sporty join a team. If you are interested in helping people, then volunteer for a local organisation.
I know this sounds daunting ontop of the academic work, but these extra things are long term and can be ongoing over the next few years.
As for academics, choose subjects that will compliment your degree. English is handy, Business Studies, History, and a language is handy incase you want to work for a firm hich practises overseas.
Good luck!!!
J x