for takeoff, at least 1 minute before initiating takeoff roll we say "Flight attendants be seated for takeoff" on the PA (the FO does that)...for landing, as part of the landing checklist, before lowering the gear we say "Flight attendants be seated for landing" (the PM does that) When they hear the gear extending they talk to the passengers (L & G in a few minutes we´ll be landing at XXXX, please keep your seatbelts fastened bla bla bla).
If something goes wrong we say "flight attendants stand by" that means they stop doing whatever they were doing and prepare for our next instruction, which could be an evac or "flt attendants normal op" meaning we were able to solve the problem and we´re not going to evac (tailpipe fires, engine fires, etc) That´s for Boeing 73CL
I think Scarebus says "cabin crew at your stations" in case something ´s not right.
Hope this helps.
SW.