It depends on how concentrated the GHB is. Liquid GHB can come in any strength. Pure GHB is a solid, dosed in grams... 1 gram is a good starting dosage, but when diluted in water, it can vary. You might find it anywhere from 1 gram per mL of liquid, to 1 gram per 5mL of liquid. You only ever find it in liquid form because solid GHB is extremely hygroscopic, meaning it absorbs water from the air very readily and quickly and turns into liquid, so it can't be stored for any length of time without becoming liquid. Anyway, it depends on strength. Usually it is weaker than 1 gram per mL, but it's best to start out with a batch assuming it is as strong as it can be, to be safe. So yeah, I'd start with 1mL and give it an hour or two before thinking of redosing. And work up from there. It's likely you'll want more than 1mL but you can always take more, you can't untake it once you've taken it. If you want to use it at a dance party, you should get some, and test it at home until you find the proper dosage, so that you don't end up taking too much or too little when you're out.