When using word-of-mouth one of the things that ensures success - and in fact with paper publicity too - is a degree of personal contact. Everybody wants to feel special. If you make sure that when you do publicity - or when you get others in each year/class/dorm/hall to talk to people - you know who you are talking to, and a bit about them... you will be far more successful. Remembering that somebody just had exams and asking how they went makes your Jewish Student Union seem like a community, and those people in it all feel valuable and wanted. Personal attention is the way to build on numbers for everything!
Different people in different years want different things. They also need to be reached in different ways. Make sure that you have people in each year responsible for publicity. Choose good people - popular people. The Jewish student organisation will appear to people as if it was all like the people they know are in it - so make sure that you get cool people. These people in each year should be given training and advice on how to get people to come (photocopy this sheet) and encouraged when they succeed. By involving them in a leadership position people become more committed - and lets face it, people are more impressed by their own mates than by strangers.
Every event needs paper publicity too - a flyer, a poster, a sheet of paper. But remember that this is just to remind people - to give people something to talk about. A sheet of paper never really changed anybody's mind. But remember the personal attention thing - a little handwritten note might get someone along. You need to be aware when designing paper publicity of who your target market is - what do they know about your event already? What do they actually want? What is it about your event that is unique? (e.g. that people are friendlier, that is with another campus / country...). You can use paper publicity to get people talking. You can also try to be a bit different - again, to see if people talk about what you are doing. The aim of all publicity is to change people's minds. The best way to do that is to get them talking.