Don't go too heavy with your eyeliner and give yourself a pat over with some powder immediately before you start. Unless you're being interviewed in studio, no-one will do this for you.
Other advice above is exactly what I'd have said. Look at the interviewer - make the best eye contact you can with them and you'll look more natural on camera. Think of them as someone who's interested, not as someone out to trip you up.
Keep your hands down -try loosely clasping them in your lap. If it's a wider shot than head and shoulders, put your knees together and cross your legs to the side at the ankles.
If it's pre-recorded and you think you've fluffed an answer, or that you could give a better answer, don't be afraid to say 'do you mind if I just answer that again'.
Do repeat the basis of the question in your answer (as somone's already mentioned) as they'll cut out most of the interviewer's questions.
Don't accept the premise of the question if it's one you disagree with - so 'Why are this years sales figures so dreadful'... don't answer with 'they're dreadful because' if you genuinely don't think they are. Say 'While area X did well, the figures for area Y are lower than we'd hoped, and we're working hard to x and y'.
Good luck OP