Book in advance

What is the normal prefered booking arrangements that providers preferr? I understand the screening aspect, but in general, is it preferred to book an appointment time a day, a few days, or even a week in advance? does it make a difference. Also, I mean this towards local providers.

Generally speaking you'll have fewer scheduling issues if you book an appointment at least a couple of days in advance. Some providers are low volume so getting a time set up isn't an issue but others go the route of quantity over quality and their schedules can be very busy.

If you're looking for a spur of the moment appointment I recommend checking out the SNATCH thread, linked below for your convenience.

http://www.eccie.net/showthread.php?t=1195043

As a local provider, I do prefer at least a couple days in advance.
I will sometimes do short notice if I'm not doing anything else that day. I like to be able to make other plans with friends outside of the hobby.