You need to accumulate a lot of knowledge about a certain thing. What kind of science are you interested in?
That is a really good question! From my personal experience, I used to be in Physics PhD program and studied physics for many years, but eventually I quit wanting to be a scientist and instead work in a finance company.
To be a scientist, you have to have the drive and curiority for the subject you are studying, be very detail oriented, patient and motiviated even when there are many many failures in your research and/or experiments. When it gets into a PhD level of research, sometimes the subject of study becomes very narrow, for example, it may not be able how the universe was formed, instead you maybe studying a very narrow field (maybe about how certain isotop was formed) in astronomy. You have to realize that your research may not be used in human lives in probably 30 - 50 years, or maybe never.
Study! Learn, and study some more! The thing about science is you must have a pure curiosity for the unknown. When one question is answered, there is always another one to ask. If this is not how you think, then this may not be a successful career for you. If you are trying to find something that is not currently available, you have to be ready to find the answers to the hard questions. Besides school, you need to be learning from other scientists and learning different environments, studying how all aspects of life affect each other. That is how you will succeed as a scientist.