What are the best ways to make a great 1st impression?
One great way is to dress nicely
You should dress nicely, not look like you just didn't care and went however you want. Now, the way you dress may also depend on what meeting you are looking to attend. If you are going for a high class business interview, you should dress the best you can. If it is not as high class, you could dress in a more casual fashion.
another good way is to look like you care
If you look like you really want the job, then you will have a way better chance than someone who looks like they don't care weather or not they get the job.
When going for an interview you always want to speak up. That doesn't mean you have to yell, just don't mumble. You want to sound like you came prepared mentally, and are not nervous.