Israel is a very informal country and shorts are fine, assuming he isn't going to very upscale places.
Yes, plugs H and C. You don't say where you are from (it helps to put the name of your country or city in your profile), but if it's North America his appliances won't work on the different voltage, unless they are dual voltage.
Advice could run into hundreds of pages, but without any clue as to what sort of "advice" you are looking for it's difficult to answer. For example, would he be using public transport? There are no cash fares on buses. There is no point in going into detail about how to pay for bus rides if it's not relevant. Taxis: the driver *must* use the meter if the passenger requests it. Locals, who know what is a reasonable fare for a journey, would happily agree to a set fare, but clueless tourists are likely to be ripped off. Insist on a proper print-out receipt (which will reduce the likelihood of a grossly inflated price). Most taxi drivers are honest, but the same as anywhere in the world, there are those who take advantage of naive tourists.
Israel is generally a very safe country. Mugging is just about unknown, but there are pickpockets, and the same as anywhere in the world, one should take sensible precautions - don't walk around with phone sticking out of back pocket, don't go down dark alleys alone at night, and so on. Don't leave bags unattended unless he wants them to be blown up by the security forces as suspected bombs. He will see plenty of armed soldiers around; nothing to worry about - they are there to keep everyone safe.
