but…"
Furthermore, keep emotions in mind and in check. Make your words sound neutral. Imagine yourself in those shoes. By the way, ideally, you should keep your criticisms positive.
And what is more - focus on what can be done, not what's been done. And don't talk on end, make a pause to let the person explain him/herself.

Note, if you don't follow these rules when giving a criticism, it may backfire, leading to a quarrel with a friend. So, be careful!