Ordered per major category.
You are a disease destined to destroy humanity. You start somewhere in the world, mostly a place of your choosing. Each country has different circumstances (e.g. poor/rich, hot/cold, urban/city or rural and so forth). This determines your start-up strengths in part (e.g. disease starting in Egypt is better equipped against heat, those in Russia against cold and so on). You should check each country while selected, click the name of the country in the world map and then left top corner the [i] box.
You can and you should evolve your disease but do so in a coordinated, sophisticated and sometimes complex or seemingly impossible ways. Your disease can evolve genes which tweak the parameters of the game either in bonus or penalty form.
Sometimes you can exploit weaknesses and/or benefits to slow or speed-up the spread of the plague. This guide is aimed to describing some of these tactics I found useful and intuitively made up. It is by no means comprehensive