If you can visualise it and give it a name you can achieve it.
Try to put into words what it is you want, what your dream, ambition, goal is. Be specific and based in reality as much as possible.
Your dream may be to perform in the West End… be more specific. What show? What role? Imagine first day of rehearsals or getting the phone call to say you got the job. Then imagine the hard work and the reward of the audience cheering as you take a bow. You could find pictures that represent your goal and print them, cut them out and display them somewhere so you see them every day.
Next, can you visualise the route to get there? The steps you need to take? Whats the first thing you’d need to do? If you’re not sure start doing research. Find out who has done the very thing you aspire to do and see where they started and what steps they took. See yourself taking that same path.
During this process your dreams and goals may change as you change or your circumstances change. That’s ok. Keep visualising and naming it and checking that is actually what you want. And keep going. Keep dreaming.