Sparrows lead dangerous lives too. They are basically bird versions of mice, at least as far as the food chain is concerned. Humans would probably leave you alone, but just about everything else — cats, ferrets, stoats, raccoons, and all manner of bigger, meaner birds — would be out to get you.
I didn't pick these at random. 
And you can't make any preparations. You can choose where you will go to sleep, and thus where you will wake up in animal form. So if you chose sea lion, for example, you could go sleep on the beach if you wanted to. Assuming you can fall asleep in weird places. And there's no magic with this part — you have to actually be able to get to the place yourself.
I think GeniusInc has the right idea. I'd probably go with mouse, and then choose to wake up in my apartment. With luck I could still use the iPhone, if not then maybe the computer. Worst case I could probably manage to scrawl some kind of note for when someone eventually came looking for me. In the meantime there is probably enough food in my cabinets to keep a mouse well fed for months. But it wouldn't take that long. If I didn't show up for work someone would eventually call my emergency contact; probably it would be later that same day if they did not hear from me, the next day at the latest. That would set the wheels in motion. At most it would be a couple of days, maybe a week if it was vacation-time.
Assuming I could get someone to believe me, it would be an easy year. But of course that's the trick. Otherwise, well, like I said, mice lead dangerous lives. Sooner or later I'd run out of food, but probably they would have rented out my apartment again before that happened. So what would I do? Stay and hope the new person doesn't have a cat? My mother's house is right down the street, but it would be one hell of an epic journey for a mouse. And there are a lot of cats in this neighborhood. Even if I made it my old (as in former, she lives at my mother's now) cat would probably kill me.
