In most circumstances, although not always, you will be considered as a tourist if you dress like one. Get rid of the fanny packs, cargo shorts, Crocs, flip-flops, and running shoes and replace them with a pair of khakis, a pair of adaptable walking shoes, and a messenger bag that can double as a day bag when in Europe. For example, even though it might get quite hot, people often don't wear shorts in Italy. Depending on where you are going you may need to cover your head and shoulders, not wear camo or army green, and even more so do a bit of research to find out what you should be wearing before heading out.