If you have a smartphone, then I recommend the free Universalis “RC calendar” app or similar, as it has the Order of Mass in a more accessible form than most missals (and you won’t have to worry about whether or not you’ll find a missal in the church). Otherwise, you might want to print off an “Order of Mass” leaflet to take with you, such as one of these: romanmissal.org.uk/Home/Texts/Order-of-Mass-leaflets
Or, if you don’t want to overload yourself and intend to just drink everything in, you still might want to prepare by looking over the Order of Mass in the next couple of days, so that you understand a little better what is going on. I still think this is one of the best presentations of the basic texts, although we now use a slightly different translation of the Latin (more literal), so don’t rely on it for the exact wording: catholic-resources.org/ChurchDocs/Mass.htm
Everything else has been said, I think? Apart from Communion, you know you can choose what to join in with? The only thing that’s usually difficult to avoid joining in with is the ‘Sign of Peace’, when everyone immediately adjacent to you will want to shake your hand and say “Peace be with you”.
Merry Christmas, and Maranatha!