How

Make sketches of the elements I want to portray, e.g. people and poses. I'll play around with possible compositions on the computer, or sometime with cutout copies of my sketches.
Take photos of flowers, leaves, plants and trees, both in our yard and wherever we go.
Create binders full of these photos and sketches, as well as research from books and online to get accurate details for the place and period I’m painting
These details include landscapes, plants, flowers, and leaves, animals, buildings, paths & walls, lakes and boats, tree species, fruit and seed pods for the elements involved.
Based on the composition I have in mind, and considering the complexity and relationship of its elements, I'll decide on the size and orientation of the painting.
Most are on birch wood panels (1.5 - 2.5" deep sides and backing frames). These are relatively lightweight and provide a strong and stable surface. I coat the front, back, and sides with black gesso - usually 2 coats on front & sides - to provide a ground layer for my acrylics. Size varies from 3x3 ft. 3x4, and 3x5 up to 4x4 ft. square.