First come, first served - if you are ready - seems to work best.

At commercial sites I have worked and flown at, launching a grid of XC
(or local racers) at a specified time also works - the commercial
instructors and students get a midday break, and the private owners
get a quick launch.

My club, unfortunately, uses a "first to sign up on the towsheet gets
priority" system that drives me crazy - since you can show up early,
move gliders out, clean canopies, help a newby, but forget to sign up
until late morning - then when you push out your glider get told "wait
in line - Joe Blow is in front of you" even though good old Joe just
showed up, signed up, went to breakfast, and is still trying to figure
out how to open his canopy.

Seriously, the tow lines fortunately (or unfortunately) are rarely
long enough to cause a problem, but the system is fundamentally
flawed.

Of course, this is the same club where the first person out will place
his glider at the very back edge of the runway (gotta have every foot
available, you know...), thereby preventing anyone else from gridding
behind him.

As we all know, the rate of change in glider club procedures can be
glacial....

Kirk
66