A long while ago, I had a discussion with someone about which approach is better when teaching others about shmiras halashon. I mentioned that people don't realize the consequences of L'H.
They replied that a better way is to mention the positive outcome of guarding our tounges like keeping a relationship intact.
I think that we should instill both approachs. The positive one motivates us to be considerate of friends, co-workers, family. Plus there is the incentive of blessings if we guard our words.
While nice incentives motivate us, what is to keep us from a huge temptation? For ex. sitting with friends and speaking and listening about somthing really interesting. - What stops us is the thought of the impact this activity can have. - It might seem at first like, "Eh, we're just talking, nothing's going to happen." But when you think about it, anything could happen, like simply one friend being upset at another friend because of a rumor that spread. But even if nothing happens, there's still consequences in the next world.
Of course, there are times when we need to say something about someone in order to protect people . That's why it's good to learn the rules of how to say it for a contructive purpose.
To sum up, we should teach both the positive things of guarding our tounge, and the consequences of not doing so.