First of all, you should know that different events demands different types of dressing. It depends a lot on the audience as well. You have to determine which kind of the occasion is and also know what will be your audience.
If you are going to deliver a public speech, then the dark blazer and charcoal grey mid-weight trousers is a good option for men while a mid-calf dark dress is more appropriate for women. However, make sure that you are dressed up in dark coloured outfit.
Always give attention to accessories that make a strong impact like ties for men and jewellery and scarves for women. It adds a decent touch to the dress and gives it perfection.
Your hair should be neatly cut and styled appropriately. Female speakers should also follow that same thing along with having a nice makeup.
An important thing that should not be ignored at all is that your shoes should be polished. Without having your shoes polished, your dressing will not get appreciation as it is an important part.
Make sure that your dress is properly cleaned if not new. There should not be any stain which could destroy the cleanliness of your suit. Stains always make you feel bad about your appearance, so try to get them removed before appearing in front of public or audience.