Firstly, it is reasonable to contact someone every 1-2 weeks if you do not know them. Statistics show that it can take 5-10 points of contact on average, before a response is received, so in this way do be persistent. However, calling or emailing someone everyday will not help you secure an interview - it is likely to do the extreme opposite and push them away. Once you have actually spoken to the person you are contacting, 1-2 points of contact a month becomes more accessible. It may be frustrating and difficult to wait weeks for a call back, but trust me it is better to wait than drive the person who you want to be your boss crazy.When you do call back, make sure the person at the other end of the phone knows your reason for calling. Do not be vague or say something cliché such as "I'm just calling to follow-up". Give your potential employer an update on your progress or if it is your first contact, tell them the reason why you are calling and how you were referred to them.If you feel confident enough to, use humour. Don't be a comedian but laugh at yourself or if, for example, you have been trying to contact someone with no avail for weeks, make a funny (and preferably clever) comment about how annoying you are being. A good sense of humour is important in this sort of situation as not only will it help you stand out, but it can put your future boss (fingers crossed) at ease. Show appreciation and make sure the person you are contacting knows that you value their time. Send a letter or email (if you have less time) to say thank you after speaking to them. Tell the person that you know their time is valuable. Make sure not to feel that the time they've spent speaking to you is a waste.So good luck with the hunting and remember - sometimes no matter how polite, qualified, friendly and considerate you are, people will not always be receptive to or appreciative of this. Don't let it get you down when people don't call you back or are rude on the phone; remember that almost all graduates are in the same boat and resolve that when you are in a position of power, you will always call potential employees back!