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. The German government were not allowed to take part in the negotiations of the treaty, and there was large-scale disappointment with the treaty in Germany. It was seen as the cause of German post-war hyperinflation by the German population, and did contribute to it considerably.
There was widespread blame being thrown around during this period in Germany. Anyone who benefited from the new Weimar Republic, or had anything to do with the military strikes that lead to Germany’s sudden loss of the war, were seen as having stabbed Germany in the back. This lead German nationalism to smoulder, and through the Nazi's antisemitic propaganda program of the 1930's, facilitated the reintroduction of anti-Jewish sentiment in Germany for the first time since the Jewish emancipation of 1848.
To further complicate matters the Treaty of Versailles allowed the Japanese to continue to colonising of China and South-East Asia, breading massive resentment in the region (especially in China), and set the stage for the coming events of World War II. 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.