We plan that if we have an appointment at 9, that we need to be there at 8:45 - by targeting a time earlier, if we get running 5 minutes behind, we still hit the appointment early/on time. We keep a list of the month's activities and appointments (stuff we need to be somewhere at a set time for) on the kitchen chalkboard so anyone can check what and when and where at any time. We discuss the week ahead on Sunday evening. We discuss the next day each evening around dinner. We discuss the day's plans in the morning.
Whenever possible, we pack up, set out, etc whatever we'll need in the morning the evening before. Sometimes, if we've got 10 minutes before leaving and we're just kind of meandering, I'll set a timer to remind myself when we need to get going - note that the 10 minutes is until we need to be getting stuff together and heading out the door, not when we need to be leaving the driveway.
We also assume that there'll be 10 minutes or so worth of stopping at traffic lights, stop signs, slow drivers, etc so if it takes 20 minutes to drive somewhere, we leave 30 minutes beforehand and add another 10 to 15 minutes to arrive early/on time. That way, if we are moving slowly or something happens last minute, we've got leeway.
We talk a lot the whole way through - "I'm going to get our shoes so we can be ready to leave in 10 minutes", "I'll help you get your shoes on since we're leaving in 5 minutes", "Is there anything you want to carry along now when we're leaving?"
Arranging things as much as possible such that departure coincides with the ending of 15 and 30 minute programming blocks (especially in the morning-DS likes to 'wake up' to familiar TV programs before he really gets going) is helpful - no need to tear anyone away from anything (and we're looking into DVR so we can record stuff).
DS often finds it helpful in making the transition from home to elsewhere by bringing something along - a toy, book, some little doodad of some form that is a 'piece of home' to provide continuity in moving from one activity/place/event to another.
Something I've found important for myself is to shower, eat and get myself ready before even waking DS (assuming we're going somewhere first thing in the a.m. which is pretty rare except for Sunday mornings). Once I have everything set, I can then focus 100% on DS getting ready and out the door and that can make a world of difference.
DH goes into his own little intersecting orbit and gets himself ready and gets stuff out to the vehicle while I concentrate on DS. If it is just DS and DH (DH is the at home parent) then (a) we try to avoid anything before 10 am (b) we prep DS the night before to know that in the morning x is happening at y time (c) we talk about what to expect, what will happen, what might happen, what could happen (d) we include him in the planning for the morning - perhaps they stop for a donut on the way or they plan to get lunch afterward or the decide to go to the park or whatever - there have been times when DS has suggested stopping at the bookstore after an appointment - that's a relaxing thing for him (and we like it too - we all just take a deep, paper- and-print scented breath and relax as we walk in the door).
Whatever it is, we try to work up a plan that fits as many needs/wants as possible. We also limit running around times so if there's a set appointment on Tuesday, there's nothing else planned for Tuesday except whatever free-form stuff gets added. We don't do back to back to back appointment running. I know that in some places, where you have to drive an hour to anywhere, that's just not practical, but it works for us.