Pop all bubbles; red or orange for DNA or the blue for research. The more DNA have, the better your disease and the easier it will be to win.
Countries
Start in Madagascar or Greenland because they are the most difficult countries to infect. Then, keeping the disease silent and wait for the entire world to get infected.
Evolutions
You can use five out of the ten Evolutions. Migrant, Cysts, Foreigners, Lethality Boost and Foreigners (or Reactive) are recommended choices.
Various strategies
Your goal is to infect as many people as possible without getting the attention of the scientists. Invest in Transmission first. It is possible to win with just the Water and Air transmissions evolved. Then, invest in Resistances, focusing in Gene Obfuscation and Natural Complexity. Have the research to move along as slowly as possible to allow enough time for your disease to destroy everything around it. As soon as the entire population is infected, evolve the first symptoms when you have at least 20 DNA points saved. One symptom will get your disease noticed, while two will start the development of a cure. Turn your disease lethal as fast as possible. Start with the Coughing and Perspiration symptoms, as they lead to lethal traits and are somewhat cheap.