For one thing it is important to get to the shuttle service stop early and line up if you want a good seat, like a window seat. There is no reserved seating with this kind of shuttle travel or shuttle airport transportation. You need to remember to bring your suitcases with you to the shuttle as well.
When using an airport shuttle services it is unavoidable that you could end up taking a lot of carry-on bags with you. Most airport shuttle vehicles are quite secure, but you still need to keep an eye on your bags, unless you have checked them in somewhere else in the airport.
It usually is a good idea to have an exact fare amount in cash when you are taking a shuttle to/from the airport as shuttle driver rarely take checks or credit cards. Some shuttle companies also allow customers to prepay for the service by credit card when they place a reservation ahead of time.
Lately there has been a trend for bus and shuttle companies to completely cover their windows with advertising, so if you like to look out the window while traveling, then be ware of shuttles that are enclosed. You can always ask airport, hotel or attraction personnel whether or not a shuttle has this somewhat annoying feature.