Casual and comfortable are the key words.  Modesty should prevail due to the many places you will be visiting are considered “holy” sites.  Shorts are great if your trip is occurring during a warm season of the year.  However, some “holy” sites do not permit shorts or sleeveless tops to be worn.  Ladies exposed shoulders are not allowed at sites requiring modest attire. Your tour host and guide will alert you the night before when short pants won’t be appropriate for the day’s itinerary.  Regardless of when you are traveling to Israel, it is a good idea to have a light jacket or sweater for the evenings, especially while in Jerusalem.  Even in the summer months it can get chilly in the evening.  Sunglasses and a hat are also a must!  Sunscreen of at least 30SPF is also recommended.   Please consult with your tour host for any tour specific dress code   requirements.