Don’t start with an apology. You’re late, your equipment malfunctions, you don’t have your materials, or whatever. You apologize in advance for how this might affect your presentation. This is a mistake because an apology sets a negative tone that may affect the entire meeting and makes you seem like a victim. Nobody wants to do business with a victim. Instead, start on an upbeat note, as if nothing is wrong. This communicates that you’re cool under pressure–the opposite of being a victim.
Don’t make personal excuses. You downgrade the audience’s expectations by offering an excuse in advance for your poor performance. (E.g., “I’m so tired”; “I got in late last night.”) This is a mistake because you’re giving yourself an excuse so you won’t feel so bad if you fail. Plus, nobody wants to hear you whine about your problems. Instead, regardless of how you’re feeling, show enthusiasm for being there and make your best effort.