I don't really agree with such advice. The only important thing is to read (or skim) many papers in the relevant field. Initially they will be hard to understan

I don't really agree with such advice. The only important thing is to read (or skim) many papers in the relevant field. Initially they will be hard to understand as they are full of difficult jargon. But after a while, you will notice the jargon that repeats across articles, be able to look it up, and ultimately understand more and more. After a while it will be fairly easy. But there is no general "paper reading ability" one could learn. Papers outside your field of expertise will always be hard to understand as long as you are not used to the relevant field, the jargon and style.