Caroline, I can't see any way I can improve on £6's answer.
SOP's are your lifeline in an airline environment, where you will find yourself flying with someone you've never even met before. You need to know what to expect of them, and vice versa. If SOP's go out of the window, at least one of the pilots is confused, disorientated and hence not contributing at all to the safe operation of the flight.
Having said that, SOP's can never cover every situation. There will be circumstances in which you and SOP will need to part company. The trick is to recognise those circumstances, keep the departure from SOP as brief and small as possible, and wherever possible
brief beforehand. Apart from anything else, in such a briefing the other pilot may well come up with suggestions you hadn't considered - keep them in the loop at all times. This is where good CRM comes in.
As £6 says, keep asking questions like that and you'll do just fine. I know that there are only two types of pilots - dangerous ones who keep trying to be safer, and dangerous pilots who don't. While I keep learning and keep applying the lessons I learn every day, I'll stay in the first category (hopefully!
). The day I stop learning will be the day I give up flying.