I did that for many years before buying a bike computer. If the number of turns isn't large, I memorize all the turns in advance. I finally gave up when I took

I did that for many years before buying a bike computer. If the number of turns isn't large, I memorize all the turns in advance. I finally gave up when I took part in an organized ride with hundreds of turns with no markings on the road. I still like to memorize the route these days. When I do that, I mostly don't use the map feature of the bike computer: I look at my speed, cadence, and heart rate.