Of course, you want to give some thought to your appearance when you are preparing to give a presentation. There are two main factors to think about:
Is my appearance consistent with the message I am trying to convey?
Is there anything I'm wearing that could distract my audience from focusing on my message?
In terms of the first point, if you are a financial manager who's attempting to get a major foundation to invest $100 million with you, then you obviously want to wear an extremely expensive and conservative suit, perhaps blue. You want to look established, not flashy, and as if you are already successful and don't need their money. However, if you are an artist who is trying to convey your own brand of quirky creativity, then wearing a blue business suit would be the worst thing you could wear. What you wear needs to communicate who you are and what you are about as much as your words do.
When it comes to number two, you want to make sure that every single element of your appearance is in sync. If you are a businessperson asking people to invest money with you and you have a conservative suit, shirt, and shoes but a Grateful Dead Jerry Garcia tie on, then your audience members are likely to be confused and scratching their heads with distractions.
One important appearance rule: Look at yourself in a mirror before you start to present. Perform one last check to see if your hair is sticking up, if there is any lipstick smudged ...