Sure, here are 13 universally applicable English sentences that could be helpful for writing essays in middle school:
1、Firstly, it is important to consider...
2、In addition to this...
3、Another key point to remember is...
4、Furthermore, it is essential to highlight...
5、On the other hand...
6、It is worth noting that...
7、In conclusion...
8、From my perspective...
9、In light of these facts...
10、Taking everything into account...
11、It is evident that...
12、To summarize...
13、Given these points...
These sentences can be used to introduce, elaborate, contrast, conclude, and summarize various aspects of a topic in English essays.