...do it NOW.
We are 5 days away from 2021.
RIGHT NOW. Stop whatever you're doing and start taking action. Start the blog you've been meaning to do, start exercising or taking cold showers.
Whatever you were planning to do in 2021, don't wait for New Years Day, start doing it now. It will already give you a 5 day head-start and you already feel the habit growing on you, once January 1st rolls around.
As a source of inspiration, I've given away two stacks of clothes to the homeless shelter to push towards my goal of becoming more minimalist. Also planned and executed a new exercise routine to get fit.