New Job Starting in 2025

I am starting a new job on January 20th (no I am not in politics). I agreed to the offer on Tuesday and will be sending in my signed letter tomorrow.

How do I continue to work through the month of December knowing I am leaving but keeping my mouth shut about it. It would be one thing if my current job was bad and toxic but its not, it's fine just need a change after 15+ years. I feel stagnant and like I am not being given advancement opportunities. This is my first time leaving a job like this and I am kinda at a loss. I won't put in my notice until Jan 6th. The later start fits better with my new company's schedule and allows me to earn my 401k match for 2024. I also have vacation from Dec 25th through Jan 5th so can't put in my two weeks until then. I will likely need the majority of the 2 weeks to find and train my replacement for my main project but the other projects should be easy to transition.

Mentally I have been making lists of things I need to do to help whoever takes over my projects. Making lists, timelines, etc. Plan to start hitting these hard next week as I wrap up some of the work for the year so making plans for next year is pretty logical.

But anyone have any tips on how to transition smoothly and not burn any professional or personal bridges? I have worked with some of these people a long time and consider them friends. Some my direct reports, I expect, will be really suprised, so any suggestions on sharing this news is welcomed.