What to avoid in sushi?

Can you tell me what I should avoid when eating sushi? I've heard there are certain things that can be dangerous if not prepared properly. Are there any specific types of fish I should steer clear of? And what about the sauces and condiments - are there any that could potentially make me sick? I'd like to enjoy sushi safely and avoid any unpleasant surprises, so any advice you have would be greatly appreciated.