My first job as professional, beyond internships, was at La Voz de Galicia, where I met a great team with Xoán González as the department coordinator. He gave me some advices that I still have in my head...
1. First of all: Rigor
During the Prestige disaster all the oil spots we placed on the maps had coordinates to set the right point. Those days, La Voz de Galicia became the reference for the information about the disaster for all the spanish media.
This is absolutely the opposite of ideas I've heard in other places: "If we just say what we really knew we couldn't fill the newspapers". What a scandal!
2. From six unities, people stop calculating
Comparing with 150 or 2000 soccer fields is nonsense. People just imagine a 'big extension', with no difference between both. Six unities is the maximum. And doing the comparison with something unitary is much better.
'As big as Spain' is a good comparison. '90 times the size of Cantabria' is not.
3. Be careful with the arrows
Don't use arrows to speak about things that are not placed anywhere. If a car is cheap, you can't draw it and place an arrow to it. This is an example of what we have to avoid.
4. Don't use too many colors if you don't need them
We have to style colors at La Voz. UA soft one (light ocre) and a other for highlights (red). What we could do just with those we do it just with those. Maybe it looks too extreme, but it created a clear code with the reader... and was also very easy to convert to B&W.
There were much more advices. But these ones stays on my mind every time I make a graphic.