Cruiselinefans is another good site. Cruise Critic is nice but there's a lot of flaming that goes on there. I have been a member for over 3 years now and I just remember to take it with a grain of salt.
I have been on NCL once, Royal Caribbean (RCI) 4 times, Disney (
DCL) 3 times and Carnival(CCL) 4 times. We like DCL a lot but do not see the extra cost to go on one. RCI is nice as well but for the cost CCL is my favorite. The food is much better on CCL than RCI.
You asked about advice, remember you do not have to do ship excursions, however, if you book tours outside of the cruiseline you are responsible to making it back to the ship on time.
Buy
travel insurance and do so at insuremytrip.com
If you can go to the embarkment port a day early, do so, especially if you are flying in.
If you drink watch the cruise newsletter you get nightly for daily specials. This will help in cost.
The surcharge restaruants are normally totally worth the extra cost.
Have fun and investigate all of the ports.
Do not try to do everything while you are on the ship. Just pick a few things. Otherwise you will stress yourself out trying to do it all.
Take a highlighter, pen, pernament marker and post-it note pads.
Make door signs to put on your door. Might sound silly but it helps to identify your cabin much easier.
I use address stickers for my cruise luggage tags. Keeps you from having to write your name and information several times.
I have made buisness cards with my name, email and aim user name to give out if I meet people I want to stay in touch with.
The diningroom serves breakfast and lunch. Some ships serve every day and others on on sea days. Normally breakfast and lunch is a bit nicer in the diningroom.
Use room service. It's fun! Plus coffee as you get ready in the morning is very nice. We tend to order coffee and juice with a pastry tray so we can have something to eat as we get ready.
If you have any questions pm me and I will be glad to help.
Be careful booking online. Always ask if you book with a TA if they have any booking, change or cancelation charges.
You can book directly with the cruiseline. If you book online with the cruise line a lot of the times you can make payments online.
Since you are looking at a cruise for someone older you might want to consider the time of the year your mother will be cruising. I would think spring or fall breaks would be a good time for her to go on a cruise unless she went with Celebrity. Try to get her to go in the off season when there are not as many kids, teenagers or young adults.