This checklist can help you tweak your posture so you can take on anything.
On point two, on crossing the arms, yes you want to appear open and approachable by having your arms uncrossed, but keep in mind when you see someone’s arms crossed it does not necessarily mean that they are being closed off, dislike you, or don’t want to be bothered by you. In many cases people with crossed arms are simply shy in social situations and are very grateful when someone comes up to them and starts a conversation.
When mirroring people be sure to delay your responses so you don’t appear to be mimicking the other person.
Quick short read, but a but needs more attention to details.