Everybody has their own ways of creating their paintings and I'd say there's no right or wrong way. It just depends on what works for you. I have several different ways of creating my artworks depending on certain factors. These could be the medium and ground I'm using, the size of the painting and the style or effect I want to eventually achieve.
I have always been in the habit of photographing the process of my paintings after each session. I find this really useful and interesting to see how they grow and change as I go along. It also helps me to see the work from a different prespective, almost like when you look at your work in a mirror. You see things you hadn't noticed before! Sometimes it can be a shock when you see that it's just not working and you need to make alot of changes. It helps you detach from it and see it as if you're someone else looking at it.
In this example I'm showing how I layed down some colours first so as to give depth to the painting and have some of those colours showing through. I didn't make any drawing on the canvas first, I just drew with the watered down acrylic paint with a rough idea of where each element would be. I then painted in oils over the acrylic under layer. I wanted the end result to be sort of hazy with soft edges and quite muted. I did this so that the bubbles would appear crisp and clear in the foreground.