[header] How to be respectful in a jewish environment [title] Familiarize yourself with the 5 main branches of judaism. [step] They are, from most stringent to least observant: chasidic (hasidic), orthodox, conservative, reform, and reconstructionist. Keep in mind that each of these main branches have several sub-branches with varying degrees of differences. 
Ask your jewish friends which branch (es) they practice and how to behave. [title] Understand that followers of chasidic and orthodox judaism, generally wear modest attire that is not overly revealing.