I'm an expert on this, having been hired a lot of times for managerial positions and even beating rivals who came from top schools--even if I came from a second rate university and even a college dropout at that.
What's my secret?
Talk and look smart. That's all. Well, it takes lots of practice, but I'm sure anyone can do it. For instance, when I applied as call center agent, no matter if I was older than the rest, I became top of my class during training.
At another time, I was chosen PR supervisor even if others vying for the position had much better credentials.
I enjoy interviews a lot, and it's during interviews that lots of applicants fail even after passing exams. The secret to passing interviews is talking and looking smart. And a big part of this is how healthy and fit you are and how good you look. If you're fit and your heartbeat and BP rate are normal. you never get too nervous. You handle yourself well and confidently. If you're fit you always look good no matter if you're not that handsome or pretty.
If you've been into aerobics exercise, you have heart and lung health. Facing interviewers will be a piece of cake to you, never getting edgy, tense and jittery when talking. Even when pressured, you talk confidently because your breathing remains even.
Compare all the above to, say, you have a bulging tummy, stooped shoulders, oily face, unkempt hair and you easily perspire and can't control your wild heartbeat because you're unfit and unhealthy.
And you know what's really annoying and brings down confidence level? Facial skin problems like oily face or pimples or acnes. They won't admit it, but most corporate bosses aren't comfy having a Ms or Mr Oily around them with red, angry acnes. In a way, it even sometimes mars company image. So they hire presentable ones. It's unfortunate and improper but it's reality.
So, you should at least prepare a month before applying for a job. Start using the right mild soap for you, preferably with kojic, glutathione and papaya extract which are proven to eliminate skin oiliness, whiten skin spots and fix scars in time. I use one and have been enjoying the benefits. But consult a dermatologist before using anything on your face.
So, remember. It's not so much your graded performance at school that matters. It's your performance while face-to-face with the interviewer.