I do a quick pencil sketch before I paint a watercolor. No matter if it's a location painting or from a photo I don't use drawing aids....I just start sketching. I paint places so I use perspective and proportion to rough things in. I try to think of all objects as shapes or collections of shapes. I think that frees you up. If you say you are going to sketch a car your brain says "oh a car that's hard" but if you think of the car as just a shape it's less intimidating. I also say the word 'about' a lot. This is located 'about' here and this is 'about' this tall. Somehow it helps me with the process.
I don't do much detail in my work so I don't think my advice will be of much use to you. There are others in the forum who do amazing detailed drawings and I'm sure they will be able to offer much better advice. I just thought I would pass along the process I use in my work.
All The Best