Travel questions and advice please?

My husband and I have no debt, no children, and we still rent meaning we have no home loan. We are in our mid twenties and want to travel. Vegas and Hawaii are easy being we live in America. I want to travel further however and broaden mine and my husbands education of the world before settling down with the whole family scene. Germany, Ireland, Venice, these are just a few of the many places in Europe I wish to go to. Any advice on travel, do's and don'ts would be of great appreciation. I was thinking of backpacking for two weeks, so any advice is accepted greatly preferably from those whom reside in those areas of Europe. Thanks!