Lately I have made a discovery for myself.
Usually I start teaching tenses for my students with the Present Simple, which is quite logical. It is the first tense you use to say anything in English: your name, your age, where you live, what you like. I thought having students understood their first grammar structure correctly is very nice. From the very first lessons, they would know how to use at least some structure in a right way. Isn't it great? No, it's not. Believe me it's bitter truth for me too.