While 1 is the present form 2 is the continuous form of the verb "to push". They mean basically the same thing because most people use both interchangeably. However, in a technical sense "you should not push yourself so hard" is right after you did the act while "you should not be pushing yourself so hard" is during the act. I hope that was somewhat helpful, if you need a more in-depth explanation just message me. -Savannah