How to get backlinks from any high PR blog

Commenting on high PR blogs can get you some real backlink juice if done correctly.
Some spam comments like the following:
“thanks a lot for your valuable sharing ,right from the beginning till end it was really very informative”
Or: “I cannot agree on everything you say in this article, but perhaps I missed some of the points you were trying to make…”By the way this last comment if searched in