Make several copies of passport and other forms of ID, keep money and personal effects well hidden, dress modestly in religious areas, purchase travel insurance, avoid Gaza Strip and Palestine territories and if you're Irish just don't go.
It REALLY depends where you go. I've been to Israel a few times and have never felt safer in my life. Israeli soldiers are always around to protect you. Unless you decide to go into the arab shook or arab town, you are really fine. The traffic is terrible though.... my advice to you is enjoy yourself immensely. And NEVER leave anything behind! if you leave your bag somewhere you'll create a huge problem, the bomb squad will be called, its a whole big deal to make sure you werent trying to blow up tens of innocents when really, you were just not being careful with your things. Congratulations and have an amazing time!
Israel is a beautiful country, as you are planning to visit Israel so make sure that you plan your trip very carefully and smartly so that you can covers all the beautiful places. You can also take help from travel agents who will organize your whole trip. As far as hotels are concerned, I will suggest you to go for http://www.shenkinhotel.com/ in Tel Aviv; they will offer you luxurious rooms along with quality service.