One of the things you really need to know is how to deal with lighting properly. Lighting you will make use of will indeed determine the whole mood of your photograph, whether it is serious, dramatic or playful.
It is a good thing that you acknowledge the need for you to deal with lighting properly. If you are able to deal with it as how you should be dealing with it, you will get the kind of mood that you want for your photograph.
Well, a photograph will be softer and have fewer shadows if taken in diffuse light. But a photograph will have more shadows and will feature drama if taken in harsh, direct light. You must know first what kind of photograph you would be happy to see after clicking the shutter so you would know how to deal with lighting properly.
You can also make use of the light coming from the great sun. But then, remember that you should avoid shooting towards the sun. Better to keep the sun at your back when shooting.
You can break all the rules on lighting. You can actually experiment, play with lighting. But then, also considering a bit what I have shared can also really help you achieve the type of photograph you want to achieve.
You can play with lighting. Know for yourself what lighting will really work best for what type of a photograph. But you still need to put into consideration the basic rules. Be guided by them on what lighting you can try for certain type of a photograph you want to have eventually.