This is a different activity from making a painting that looks just like the original. If you notice, for example, that the artist chose to wet the paper before applying the first wash, and then proceeded to make big, confident, fluid strokes, you should do the same. If you make similarly bold strokes, they WILL NOT be identical in appearance to the original. How could they be? The only way to get them to look just alike would be to make many, many, very small and extremely careful strokes. I repeat, the purpose of the exercise is to understand the choices that an artist made. That, and to practice asking the questions that make your own choices deliberate.
Look for a watercolor landscape that you admire, and take your time tuning in to the artists choices. What matters most? Make a version that feels like the original.