I love starting a new picture, first of all working out the proportions and tweaking them to fit exact divisions, ie half, quarters, fifths, tenths etc. I then move on to the perspective working out all the angles, then the light, sometimes its better to have the light coming from a different direction to improve the picture. I know a lot of people like to just dive in and get on with the painting. Canaletto used a pinhole camera to do his preliminary drawings and was never accused of cheating. if you like to get a quick start have a look at the app `Artist's Eye Free' for phone an tablet it won't give you a perfect sketch but can give you a good start on proportion and perspective. happy painting..