First, I'd make sure the shrinkage is reversible. If it's a one-way mission to germhood, I'm out! Assume it's just a sci-fi fantasy, a thought experiment or -- as Einstein might have put it -- 'gedankenexperiment'. This brings to mind old movies like 'The Incredible Shrinking Man' or 'Fantastic Voyage'. There are also physical conceits straining plausibility, including scaling effects that reduce your size by 5 orders of magnitude -- from 2 meters tall to, say, 20 micrometers, the size of a white blood cell. You'd feel very strong and would hardly notice gravity, but forget about how you're going to eat and breathe using your body chemistry in a world where native molecules are 100,00 times too big!. Also don't worry about how the surface tension of water might rip the skin right off your body, or at least keep your arms, legs & body stuck together. Etc, etc. Here's an idea of what the cellular world might look like, based on cutting-edge science (wonderful animation from Harvard): http://multimedia.mcb.harvard.edu/ (watch video of Charlie Gibson - ABC News) In the real body, however, everything actually runs much faster, and they don't show all the 'jiggling around' due to Brownian motion and quantum effects. Anyhow, I have an interest in curing disease and aging, so I'd get a close look at the insides of coronary arteries to see how plaques form and might be prevented from doing so. I'd navigate to the brains of Alzheimer's patients & get a close look at the beta-amyloid plaques gumming up the works & see what to do about it. I'd try to see how damage from stroke might be repaired. While I'm in the brain, it would be nice to catch a glimpse how memories are stored. This is still a huge mystery in neuroscience. Proteins, nucleic acids, synapse patterns, or 'other'? Or all of the above? I'd look for cancer cells & see what really makes them tick. Figure out how to take them out early. Additional biological insight (genetics & epigenetics) would come from observing a first-trimester embryo developing in a mother's womb. See why collagen breaks down in elderly skin, making our young faces wither with age. What happens in the brain to make us forgetful & how can it be prevented? The list is endless. What's amazing is that biomedical research is starting to answer these questions using full-sized scientists who don't have to be shrunk to see some of the details -- though medical progress would occur much faster your way!

I'd go inside my brain and see what the hell is REALLY going in there. >_> Then I'd run around in my veins, it might be fun, like a water slide. :D