You have choices. Do you book everything beforehand or try your luck when you get there? I do both. In general, if you are at all anxious about traveling alone, go ahead and pre-book. My go-to sources are http://www.tripadvisor.com/, http://www.vrbo.com/ and http://www.airbnb.com/search , all sources online.
If you plan to wait until you get to your location, you might want to ask on a travel forum like http://www.tripadvisor.com/ whether there is a lot of availability in city X when you plan to visit. As a woman traveling alone, I prefer B & B’s. They are small and the owner not only lives there, but invariably takes a personal interest in your welfare. I’ve had owners do all sorts of things such as have a grandparent pick me up for free at the airport, store leftover food from a cooking class in their refrigerator and then reheat it and serve it to me, take me to a bus station, buy the ticket for me and then wait until I got on the bus, lend me their personal alarm clock set to the time I needed to get up. I could give more examples but you get the idea. I also mention to the owner that I found their place on Trip Advisor. I don’t know for sure if this helps, but owners are very dependent on these reviews. I also mention that I write reviews when I get home, and I always do.