Take advantage of the night-before package:

I simply cannot think of anything to enhance your cruise vacation more than arriving the day before, especially if you are out of state and have to fly in. If you have kids with you, then you know how easily they get tired out. That rest period is going to be well worth what you pay for it. This also holds true if you drive to the ship - of course, you will find your own room the previous evening. Unless you live in the vicinity, I'd recommend that if you have to drive 4 hours or more, arrive the night before. Most locations have parking at the cruise ship terminal, but it can be expensive, up to $20 per day. A little known alternative is that many hotels offer free parking for up to 14 days; all you have to do is stay the night prior to departure. And the usually offer shuttle transportation to the cruise ship. A night-before stay and free parking is probably a deal that cannot be beat, but check a head to make sure the hotel's shuttle isn't broken down, and also, what limitations there are (how many times they make the trip on cruise day, etc). If the shuttle isn't what it is supposed to be, you can probably still get out cheaper by parking there and taking a cab to the ship on your own.

Should I buy airfare and night-before packages from the cruise line or do it myself?

For the first trip buy everything from the cruise line. Air fare might be a bit more expensive, and your flight itinerary might take you on a hop or two, but transportation to AND from the ship is included, as well as to the hotel the day before. After the first cruise, then you know what to expect, and you can decide for yourself if you want to get to the ship on your own or through the cruise line. Also sometimes you can buy a local transportation package to and from the ship from the cruise line and book your air fare on your own, so at least check on that availability. Otherwise, you'll be trying to flag down a cab to the airport in competition with everyone else that just got off the ship. Also, in Miami at least, many of the hotels offer their own night-before package with transportation two and from the airport and ship, so that is yet another alternative. But again, there is a bit of logistics involved with this, so my recommendation is to purchase everything from the cruise line for your first cruise.