Regarding offices, let the receptionist know who you are and why you're there, then sit (i.e., my name is X and I'm here for an X o'clock appointment"). Regarding meetings, if you are a presenter in the meeting or are very likely to be talking at some point in the meeting, sit at the table. If you are an observer, sit away from the table unless someone invites you to the table. If unsure, sit away from the table until someone invites you to the table.
Try not to walk with your hands pointing outwards. Try to keep your arms and hands relaxed.
When you are walking in a crowd or walking toward a stranger, look at the feet. This will be a better indicator of the direction someone is heading than the face or upper body. If you're walking toward someone you recognize, nod and say "hi". It's OK if the two of you become confused as to where the other is going. It's actually funny, so laugh. You can even say, "Want to dance?" unless the other person says it first.
I hope that helps.