又 is used in declarative sentences and describes the simple repetition of actions. This repeated action has already occurred once in the past.
S 又VO了
北京昨天下雨了，今天早上又下雨了。
再 is used to express something that has already happened and will happen again.
（S） (想/要)再 v # mw + noun
早上我喝了三杯咖啡，现在我想再喝一杯咖啡。
（S） (想/要)再 v # 次
我去年去了中国，今天寒假我想再去一次。
However, when there is 要，想，or 是，you should only use 又。
Subj. + 又 + 要/想/是 Verb + Obj.
昨天考试了，明天我们又要考试。
早上我喝了三杯咖啡，现在我又想喝一杯。
怎么又是你？(How come it's you again!)
昨天我背（bèi，to recite）课文，今天又是我背课文。
reference
https://resources.allsetlearning.com/chinese/grammar/Comparing_%22zai%22_and_%22you%22
