Here are some real world Do's and Don'ts:
1. Dress appropriately for the type of position you are applying for (business suit for exec., shirt/tie for research or engr., etc.)
2. Do not discuss employee benefits unless they bring up the topic, and even then, minimize your questions on them.
3. Do research the company NOW and know some basic info. that can help you answer questions on their mission, product, and customers, etc.
4. Don't over sell yourself with too much talk, yet provide necessary, pertinent information
5. Don't dwell on your lack of job experience being a graduate, maximize your time in explaining your talents, knowledge, and eagerness
6. Do try to work in the concept of you being a "team player" as most companies welcome that mind set
7. Don't let them trap you into discussing wages unless you are offered the position in the first interview (doubtful). Tell them that you are prepared to put forth 110% in return for a rewarding experience with them and that you would expect the salary package to be on level with that type of position. Wages can be "negotiated" more in detail during a second/third intrvw.
8. Do inquire from them as to an approximate date of hire, and how much time they will give you to acclimate to the position.
9. Do send a followup letter of conversation & thanks immediately after the interview, and mail it that day, keeping it brief and noting any key issues they may have doubts on of you or spent considerable time discussing with you. Reinforce your capabilities in those areas but keep it brief. No more than 1/2 page letter is sufficient.
10. Do be polite, repeat their names aloud, as they introduce themselves, be natural, and leave a positive impression of self-confidence and flexibility.
There's always the chance that a company can choose a candidate that might not do that well on an exam in trade for someone that they feel is the right fit for their organization... with hopes of allowing you time to brush up on knowledge, etc. Browse the internet for more advice as there's lots of it out here. Also, there are web sites that provide sample letters. If you are offered the position, even if it's over the phone at a later date, you should still write a letter of acceptance and of gratitude to them. I hope all this helps you land a good job.
NOTE: I don't know your location, but here in the states, there are soecific questions an interviewer is not allowed to ask a candidate such as those dealing with race, religion, family, marriage, political, etc. They do get around it though by wording questions that will have you answering in such a way that it "suggests" the obvious. It's best to avoid even talking about religion and politics. Leave that for the lunch room once you're hired and even then avoid it since it often comes back to bite you or change worker relationships. Avoid the two topics like the plague!