People! Help me dress myself!

[ZackL]

So I managed to get a job in my new city and its the first job I have ever had requiring a shirt and tie (electronics sales, pretty cool I am in the TV and audio department... got the job because I knew more about the stuff they had then the guy interviewing me). I don't want to look like a complete moron, so I have a few questions. I went to a suit store and a girl helped me pick out some stuff but I was still wondering:

Does a tie go to your belly button or your waist? Is the most common knot to use the one where you spin it around the skinny part twice and pull it up then down the hole in the front?

Can I wear black pants with a black shirt as long as my tie isn't black?

Is there anything black pants DON'T go with?

Is there a rule when wearing a tie with certain shirts? Like should a solid tie go with a striped shirt and vice versa? I don't know?

Thank you.