Well, you have to ask the right questions. What is bothering you with the file above? Do you not want the lens flare? Do the clouds look flat? Too much fog or haze? Just open the atmosphere tab & move the sliders, it will change the lighting setup! Give the plant some landscape to sit on, this will damp the lighting & throw some shadows up around the place. If you want a step by step tut, go to the backroom & follow something from step one to step twenty or whatever. It may take hours, even days. You will be learning all the same!