Secondary screening and where to sit

I am flying to Miami in UC on VS05 on Wednesday. I have a seat reserved in the nose just a couple of rows back. Is this preferable to upstairs? And on the way back when I may want to sleep?
And can anyone tell me what secondary screening is once I arrive in Miami and how do I avoid it?
And can anyone tell me what secondary screening is once I arrive in Miami and how do I avoid it?