Come on over to Moving Up for your primary help and Q&A source.
"A wizard is never late, nor is he early. He arrives precisely when he means to."
I either quote everything if that's what I'm replying to, or I clear the quote and leave the necessary section remaining. For example, if someone had multiple questions in their post;
Does anyone know anything about Destiny yet? When are Bungie going to reveal some details? I've been gone for a long time and I have no idea what's been going on... Also, any news on Bungie day? Yeah I missed that too
If I only wanted to answer the last bit, I would quote & respond:
Posted by: Example
Also, any news on Bungie day?
They just gave us some new Avatars and stuff
Not a great example but you get the idea.