First, I would take my time to learn the art of painting.
After a few years of practice, I would go find a cave or an underground facility. Something that is big and can withstand the test of time. A missile silo or something like that.
Inside that facility, I would find a long hall. Bringing my paintbrush and plenty of paint (and time), I would "write" a message to whoever is the next ruler of Planet Earth, be it an evolved animal or extraterrestrial alien.
On the left side of the hall, I would paint the story of mankind from its conception to its untimely demise. An abridged version, but one that would give a big idea of how mankind came from Ethiopia and spread out to rule the world.
On the roof, I would paint scientific information. Calculations made about the Sun's expected timeframe (scientists suspect Earth will become uninhabitable ~1 billion years from now), the table of elements, the atomic model, etc.
On the back of the hallway I would leave Latin textbooks with basic tools for a most likely illiterate entity to learn the language of science. Extensive books packed in an environment where they could be preserved for millions of years. And on the right side of the hall, in Latin I would perhaps write a poem or simply the greetings from the last man on Earth. After that, I don't know. I would probably dedicate my life to science and do things that I have always wanted to do.