I normally do few detailed pencil sketch of the subject that I am going to paint. I draw the grid first on the paper and use a similar grid on the photograph by using the grid and scale tool which is an inbuilt feature in most photo applications.I then start to draw the subject on a paper where I have drawn grid from a grid photograph or add in the elements (could be from multiple photos taken) that I wish to include in the composition. By using grids, I keep the elements in perspective and sizes in proportion. It also helps me to keep drawings accurate which is essential for realistic painting. I then go on to shade the entire picture using few graphite pencils which constitutes value study through which I will know the lights, darks and the mid-tones of my subject.
This stage seems time-consuming but I find it necessary and useful.
I keep the layout of the sketch similar to that of a watercolor paper so that it’s easier to visualize on the actual watercolor paper. This gives me a preview of my final artwork or indicates me what my final artwork might look like and makes it easier for me to choose the composition that pleases me the most. While I am drawing and sketching, I start to observe the details and think of colors that I am going to use or sometimes even start analyzing the techniques to paint certain features in mind. This helps me to know the subject or connect with the subject well before I even start painting. This, in turn, makes me feel confident when I actually start painting.
Once decided on the composition, I redraw on actual watercolor paper using the same grid method. This stage seems easy as I already have measurements and the composition ready.