The muster drill is a USGC requirement; usually prior to setting sail they will clang the klaxon [another nautical term for the annoying buzzing-farting-belching sound] and tell everyone to return to their staterooms, grab their lifevests and report to their muster station. ...your muster station is listed on the back of your cabin door, and/or inside the closet where your lifevests are.
Do not put on your life vest; just carry it. Do not drag the straps. Do not carry any drinks, snacks or beverages. They will make you throw them away or leave them behind -- although I personally believe the muster drill should have a two drink minimum.
Follow the arrows for your muster station. When you arrive, a member of the crew dressed in a day-glo orange or green [I forget] jacket and cap will instruct you to line up. Do this as quickly as possible, because the whole thing is annoying and the sooner people line up, the sooner the crew can report that they are all set, and the captain can let everyone leave.
While lined up, you'll be instructed what to do during a water landing, how to use the seat cushions for flotation devices, how to put on your lifevest, where the emergency beacon is on it and the whistle. [Don't play with them]. After every passenger has gotten there and they've gone through the emergency procedures [which you will forget], they will tell you to take the lifevest off [while buzzing that damned klaxon some more] and return them to your cabin.
Again, do not drag the straps. There are old people who do not walk so well and they don't need any extra tripping hazzards. Get good and lit beforehand. Doesn't hurt and helps pass the time.