Want to get into the exciting (and lucrative) world of investment banking, but don't know how? Ex-Goldman Sachs banker Peter Harrison has all the answers.

A candidate is 30 years old and is looking for a career change. Do they have any chance of making it into a role in investment banking?

Yes, of course you do. Obviously, the more qualifications you have and more relevant your work experience, the easier it will be. If you are 30, then you are competing for associate positions with the MBAs from Harvard Business School. It is going to be tough, but achievable.

Which roles are most likely to be open to someone in this situation?

Any roles which are not revenue-generating are going to be much easier to get, but you will probably want what they refer to as a 'front office' role where you earn the big bucks. Trading is really, really difficult if you are not very numerate indeed. Sales is one of the easiest. Corporate finance/M&A, along with research could be possible if you have knowledge of a specific industry. Private equity will be the most difficult to get into.

What can they do to maximise their chances of success?

Get extra qualifications relevant to the business area you are targeting so that you can show you are someone who has gone the extra mile and can be taken seriously. The qualification itself will not give you the practical knowledge you need to do the job, but it will be useful in getting you interviews and enable you to talk the talk when you start meeting professionals for informal chats with a view to getting them to help you get interviews. You then have to use a combination of applying to job adverts (least likely to work), recruitment agents (somewhat likely to work) and networking with professionals (highly likely to work if you do enough of it).

Where do most people go wrong?

Most people do not use a cover letter or resumé that is as effective as it needs to be ( Helpmegetaninterview.com are the specialists for City resumés and cover letters). Candidates often just send it to HR people at banks which is pretty much guaranteed to fail if you do not have relevant experience. They then think that they will not get a job in banking, without realising that emailing HR was never going to work in the first place.

Which are the three most common reasons for instant application death on a CV?

First, not having relevant work experience. You cannot fix that if you do not have it, but you need to recognise that this is the most common reason for instant death. Second, unimpressive academics. Third, a resumé where it is not easy to figure out how impressive you are. Only around one fifth of resumés I see genuinely make the most of whatever achievements a candidate has. The professional re-write of a CV is really always worth it, but even more important is the cover letter tailored to the business area you are applying to. In the cover letter world, one size does not fit all! It has to be tailored or you will not come across as understanding the business you are applying to.

And...which are the three most common reasons for instant application death at interview?

First, not building a personal rapport with your interviewer. This is why sales-types are so much better at converting interviews into job offers and geeks find it difficult even though they may be smarter and harder-working. Second, taking more than 90 seconds to answer questions and not getting the interviewer into a conversation. Third, not having technical knowledge of that particular business area.

• Peter Harrison is founder of Harrison Careers, a company devoted to helping candidates land roles in investment banks.