Pre-planning - we selected our cruise line and ship and itinerary based on 4.5 star ratings and above, # of ports and duration at each port.
A group of about 15 of us (ages 26-60, mostly first time cruisers) went on the Royal Caribbean Freedom of the Seas in January 2008. We stayed at the Marriott Towneplace Suits in Miami the night before our departure. It was a pretty decent hotel and close to the port. The drivers dropped us to the port, and returned their rental cars to Alamo by the Airport (most of the group had been there for a week prior so they had all rented cars). They took the free shuttle back to the port and we all boarded by about 1:30pm. The check in process was very smooth and didn't take very long - we had done the on-line check in a few weeks before.
Note on TIPS - online check in asks whether you want to settle everything with your credit card or with cash. We selected cash, since the US/CDN exchange rate was good but we were confused about the tips. The way it works on this cruise line is that you are given envelopes in your stateroom a few days before the cruise ends. You have the option of putting cash in there yourself, or paying with credit card at the customer service desk. Then they will give you "vouchers" to put in your envelopes so you can present these envelopes to your server, room attendant, etc. with either the vouchers in them or cash.