So just watch the video. Particularly how quick and deft he is at making a Nerf Gun look real. I find him a little funny and very good. He is or was one/half of Myth Busters.
When he is adding paint he says not to make it too regular. When I paint trees or foliage I do it quickly and with various colours. The quicker the better. I need to stand back and look at the result often because regularity creeps in. As humans we are very good at making things regular/consistent/continuous. Nature isn’t like that so a lot of my art training involved making areas that I am painting look less regular and thus more realistic.
Inexperienced artists tend to make their work much too regular. I believe this is a learned behavior in both directions; perhaps an evolved behavior. In order to see a lion in the grass we have to make sense out of what we are seeing and this usually involves simplification so that the lion matches an inner image that we have. I think I have finally got to a point that I can slap together some paint in a way that might look real. Perhaps we need to thank the Lion for art as we know it.