Priority checkin is NOT offered to Gold level Crown & Anchor members on RCI, only to Platinum or above level. Gold is actually the 'starter' level, awarded after your first cruise, and lasting until you have completed 5 cruises, when you are elevated to Platinum. That's when priority checkin comes in. After 10 cruises, you become a Diamond member, then after 24, you are Diamond Plus, and get to take the Captain home with you after the cruise.
The only way I know of priority boarding is to book a suite or to perhaps have cruised with one line so often that you achieve "Gold" points standard for example. We have been on Brilliance and it is the most fabulous, beautiful ship. However the food was very bland and "American" - not a patch on P & O. We have had priority boarding everytime with P & O by booking a mini-suite or full suite. We also have priority disembarkation as well, being the first to get off at the end of the cruise is worth the extra. Priority boarded passengers also have sandwiches and champagne etc. whilst waiting for the cabins to be finished. Hope this is helpful.
Priority check in is normally only awarded to Crown and Anchor members with Gold or Platinum status or by booking a suite. You can check with RCI/Celebrity head office if you have special needs or look at their web-site. If you have priority status then signs will show you where to go at the dock but with Radiance Class ships boarding is not as arduous as it used to be and the systems generally work well. I would disagree with the previous answer writer in that I found the food far better than P&O although not as good as Celebrity's. Brilliance is great and Radiance Class is unique in its shape and layout, if you haven't been on it before you are in for a trea.