And I wonder why I get hesitant to have casts for my films
..................
Moral of the story-don't tick off your cast unless you want to do a solo
)
Indeed, make plans and schedules.
Nobody likes uncertain schedules.
Storyboard your scenes: this will help you visualise the movie, but will also help communicating your ideas (and it will save time during shooting). Don't forget to note the important things: at the end of the day you will probably forget the things you didn't write down because you thought you would not forget it.
Do you have experience with shooting a film?
If not: write a short simple scene, based on dialogue and on 1 or max 2 locations (maximum 1 day) to practise filming it and get some experience. Don't forget to make a timetable for the shoot and note the times during the actual shooting: this will give you a better view on the time it takes to do something.
Try to work with the crew you want to make the zombiefilm with: this way you get to know each other and you can learn from mistakes.
Don't forget to edit it: this might give some insight on what could have been shot differently.
Practise the carscene (the lighting)!
This way you can set it up easily and save your cast and crew frustration.
Test shooting at night: does it give you the look you want?
Do you see what you want to see?
Or do you want dark blue skies? In that case: rehearse before sunset, shoot during dusk right after sunset. You will only have a short period to get your shots (also depending on the season and your location)
It's what I did for a few shots in this 'short':
http://www.youtube.com/watch?v=NUQC9-PH_KA
Make sure you know what to do, before your whole crew & cast are waiting.
Good luck!
And don't forget to show the result of your efforts