In 1995, I first went to Europe to race. It was my third year racing and I was cat2. The very first ride I did was and easy two hours with a group of ten Belgians. We rode 2 abreast and talked during this easy spin down one of the canal paths.
I learned more about bike handling that day, than all 3 years of US racing combined.
We rode so close to each other, that our shoulders were literally bumping the whole 2 hours. At first I thought, why don't we give some space and just relax, but then I realized these guys had been taught for years on the art of technique.
I was thrown into the fire and learned quickly how to ride in very close quarters. No drills needed. Just ride tight at all times. After a while, it becomes very natural and it also keeps the traffic from being delayed on busier roads.