It is okay to say, "I do not know." or "I need to do some research and get back to you."
If you have ANY hesitation about making a change to a production system, DO NOT MAKE IT. We all have shot ourselves in the foot at one time or another. Learn from our mistakes. Do not be that guy (or girl).
Until you get good at estimating how long it takes to complete a task or project, double your estimates when someone asks you how long it will take you. It is better to over estimate and get it done sooner, than to under estimate and have people waiting on you. (BTW - Any non-trivial task will ALWAYS take longer than you think it will.)
Before making any changes, make sure that you have a good backup and that you have tested your ability to restore it. Yes, it will make things take longer but it is better to have a fallback position. This is doubly true in production. NEVER MAKE PRODUCTION CHANGES WITHOUT A BACKUP.
Be humble. The days of being a jack of all trades IT practitioner are dead and gone. There are too many things to know and not enough time to learn them all. By and large, IT people can be cooperative and supportive.... if you are humble. If you act like you know everything and fail to ask for help, you will find everyone lining up to watch you fail and snickering at you when you do. Check your ego at the door, learn from others and when you have the opportunity to, help others out when they ask for it. Do not be that dick who tells everyone to RTFM. Having said that, if someone asks the same question over and over again... feel free to tell them to RTFM. Nothing is worse than a freeloader. We all have jobs to do and while helping new people out is part of the job, doing their job for them is not.