There are a few different aspects to this and it’s not as obvious at it may seem at first.
Personal hygiene
The obvious part – shower, clean hair, brush teeth, gents - clean shaven, deodorant, subtle perfume or aftershave.
Don’t over power them
Do not overuse the deodorant, perfume or aftershave. Keep in mind that the more you use a product the more accustomed you become to the smell of it. You essentially become immune to it, so you inadvertently end up putting more on over time without realising it. Generally those around you do not notice as the change is gradual. However people you meet for the first time in a confined area may well find the scent overpowering.
On interview day back off – use less than you normally would. Do not be tempted to splash that bit extra on just for good measure.
Lingering lunch
Try not to eat right before the interview. If you find that you do not have a choice make sure you do not eat or drink anything right before the interview that may linger on your breath – i.e. onion, coffee etc. Avoid foods like burgers that may repeat on you (especially if you eat them quickly). Eat slowly and chew your food - this will reduce the chances of an embarrassing 'food repeat' during the interview.
Smokey Joe
Do not smoke before going into the interview. Interviews can be stressful and you might need a ciggie before you go in, but try not to have your puff just before you walk in the building. The smell lingers and interviewers will smell it on you. It shouldn’t, but it may go against you, so better safe than sorry and no smoking within 30 minutes of the interview. – and make sure you have your last smoke in an open area (ideally not surrounded by other smokers)
Final freshen up
Before going into the interview have a mint to freshen the breath. Chewing gum is an alternative, but make sure that you find a bin outside the building and discard the gum before you go in. Interviews are a No Gum Zone!
If you get the chance just before the interview it’s a good idea to pop to the loo and wash your hands – and I mean wash your hands!