Israelis are very conscious of safety on the streets - Tel Aviv is no exception. For one thing, don't take photos of military-related buildings (due to tense Arab-Israeli relations) - you risk attracting the attention of the Shabak service.
Second, never touch bags or packages left unattended on the streets of Tel Aviv. If you plan to visit synagogues or other places of worship, respect tradition by covering your legs and shoulders.
Basically, these are all the precautions to remember in Tel Aviv.
