Some mail programs automatically place your reply above the quoted text, and some place it after. The industry appears to be moving towards placing your reply before the quoted message. That way, you don't need to scroll down through a long quoted message to get to a reply, but it's there if you need to refer to it. However, if your mail program puts the quoted text first and your reply second, that's fine too. Additionally, different mail programs have different ways of indicating quoted text.
Some programs use other characters, and some indicate the original message with a divider line.
Whatever the method, be sure that it is clear which text is the original message, and which is your response. Your comment about the second point goes here For those of you whose programs do not have a function for quoting replies, or if you just prefer not to set it as a default, you can try a few other things. If you need to copy text into your message to quote it, or if your Email program does not identify quoted text with angle brackets or some other method of identification, please make it clear which portions are from the original message and which are your replies. This can be easily done by putting double angle brackets at the beginning and ending of the quoted text. This was the original message that I am replying to, or a part of it.