Well, that's a hard one, even harder than ser/estar. I think there's no easy way to explain that, and there are no rules to cover all cases, but you can take a look here, its the best explanation I've found about this. http://www.studyspanish.com/lessons/porpara.htm I hope you found it useful!

With "para" ¿Para que pierdo el tiempo en esta red llena de perfiles falsos? with "por" ¿Por donde hay que ir para dejar de ser un pobre diablo sin un dolar?

Hello from spain , I would like practice english with your help, I stuied physical Education and I can teach you spanish We can práctice If you want. Hola,desde España, me gustaría aprender inglés contigo. He estudiado maestro de Educación Fisica. Podemos practicar si tu quieres