If you fail a subject does it have to be on your c.v.?

A c.v., or resume, doesn't normally include individual courses taken in a degree program. In general, you list only degrees earned and where you earned them. If you earned enough credits to graduate, you do not have to give any specific information about any courses you happened to fail.

However, if a prospective employer or educational institution asks to see a copy of your transcript, you won't be able to hide the information.

My advisor said they should always look positive and not to put in anything that looks dubious. And if you failed a course it doesn't get a certificate, although you will need to explain what you did for the time you were studying if full time. But it's far better to pass something after and then no one cares what you failed on the way as it happens to many people before they succeed. But it's not normally a requirement.

You don't have to list the courses that you took, but you should mention the degree that you earned. That being said, you ought to place your GPA on your CV as well, although if your GPA is not spectacular, don't include it. However, if you are asked, and you greatly inflate your GPA during your interview (i.e, you GPA is a 2.0 and you claim that you earned a 3.0), that might be seen as fraud. But, if you say that you earned a 3.0 and you really earned a 2.8 or 2.9, that might be seen as just rounding to the nearest whole number and your future employer might find that acceptable.

That being said, it does not bode well for you to outright lie to a future employer, in the end it will come and bite you. Do not include employers on a CV that you never worked for, and do not include responsibilities that you didn't have. If you employer checks your background and speaks to your past employer and discovers that you lied, if you were given the position, you could be fired, and if you are still in the interviewing process, you will not be given the position.

Accentuate your positives, diminish your negatives, and if you can, try to make your negatives work for you during your interviews.

During an interview, wear a suit if you are a guy, wear a pant suit or business dress if you are a woman, even if you are dressed better than the person interviewing you, you are showing them that you can be taken seriously and that you take the opportunity seriously.

Don't use slang, use proper English. Turn your cell phone off, and if it rings, don't answer it. Don't text your buddy during the interview, and don't talk about money up front, even if they bring it up. If an employer discusses money, you can say, "you are a competitive firm, I'm certain that you can offer a competitive salary."