I always travel alone, I tend to spend most days alone doing what I want then chill out/go out with folk from the hostel in the evening. For me that's best of both worlds. I would plan a bit, you want to make sure you don't miss stuff you'd have loved cause you spent all your time drifting around with others. You also don't want to be too dependent on others, some days there'll not really be anyone about to do stuff with and you want to be able to still enjoy your day.
Book hostels through hostel world or hostel booker, they cover most and even if you just do it the evening before, it makes life much better if you know you have somewhere to sleep when you arrive. But if you can book sooner, in a lot of cities the decent ones sell out, especially at the weekend.
Not sure what else to tell you but ask any specific questions