Probably the biggest thing is to let them know what’s going on. At LGA? Warn them to use the lav prior to push. It may be a 10 minute taxi, it may be a 2 hour taxi. Weather delay? Let them know. MX? Give them some information, but not too much.
Tell them where they are going. If you are going to a place like Portland, ME, emphasize that you are not going to Portland, OR. (Panama City, FL, versus Panama City, Panama; Albany, GA versus Albany, NY). Yeah, it happens.
Don’t lie.
Don’t throw the company or someone else under the bus, but again. Don’t lie.
Don’t be like the crew from my DH last month. We get pushed. Sit for 20 minutes. Then the airplane moves.... back to the gate. Jet bridge gets attached. Gate agent comes down and tells us there is a MX issue. We deplane and the entire time not a peep from the cockpit and the door stays closed forcing the FA and gate agent to deal with it.