In Israel the bus driver is always responsible for validating your payment, whether you pay in cash, with a paper pass or using a Rav-Kav smart card.
Read this if you're planning to travel in the Tel Aviv area.
If you plan to travel multiple times for the same fare, you might consider buying a kartisiya (a miltiple ticket) from the driver. A kartisiya allows X journeys for a discounted price. Traditionally a kartisiya is a piece of paper, and a hole is punched in it by the bus driver every time it is used. The paper kartisiya is being phased out, and now in some areas of Israel a kartisiya can be loaded as a contract onto a Rav-Kav card.
Monthly passes exist in many areas of Israel and can be bought around the 1st of each month. Most monthly passes are only valid for some of the bus companies that operate in that area. Some monthly passes are sold as paper tickets, while others are loaded as a contract onto a Rav-Kav card.
Daily and weekly passes exist in some cities, but are less common.
Senior citizens get a 50% discount on all tickets and passes. Children under the age of 18 get a 50% discount when using a kartisiya.
The Egged website contains an extensive section about [* http://www.egged.co.il/Eng/main.asp?lngCategoryID=2664 tickets and discounts]. As the fares and tickets are regulated by the ministry of transport, this information is generally true for all bus companies.
The [* http://rail.co.il/EN/Pages/HomePage.aspx Israel Railways] website also contains information about tickets. Note that whenever the website mentions combined tickets between Israel Railways and Dan, it actually means not only Dan, but the four bus companies Dan, Egged, Kavim and Metropoline, whose fare system in the Tel Aviv area is unified.