Question 343056
It's hard to say without a specific example.  Basically, you look for things you know are true, that will lead you to the desired conclusion.  Whenever you write a geometric statement, like "AE=ET", then you have to give a reason for why it's true, like "definition of midpoint", or something like that.  Please check out my facebook page, Kate Calendrillo, tutor.  Post your question and I would be happy to get back to you ASAP.