Not to impose unrealistic sanctions, reparations, or tariffs on a country to damage their economy
The Treaty of Versailles was the treaty signed at the end of the WW1. Article 231 of the treaty forced Germany to limit its military capabilities, give up its colonies and some territory, and to pay massive reparations to the Allied Forces. This was thought to have caused the post war hyperinflation by the German population and did contribute to it to a large degree. This then caused German nationalism to smoulder and was the beginning of anti-Jewish sentiment in Germany.
Reparations such as these or similar economic sanctions breed isolation, backwardness and contempt, and should be used as a last resort as they only worsen international relations.