This isnt something I am preaching, its just something to remind myself –

1. Never step into customer’s territory, dont tell him how his business could do better.
2. Just be precise whether what he wants can or cannot be done, dont get into better approaches or alternatives unless asked for.
3. Learn to keep quiet.
4. Learn to talk only when talked to.
5. Learn to hold your opinions and your facial expressions.

You should do well !!!