I have used GBL at dance events roughly once a month for about a year. I am going to describe exactly how I approach it because I think the substance gets either demonized or treated too casually, and neither helps anyone stay safe.
I measure every dose with a 1ml oral syringe (no needle, obviously) that I keep in a small case with a bottle of juice. I never eyeball it. The difference between a pleasant dose and losing consciousness can be as little as 0.3-0.5ml depending on body weight, stomach contents, and individual metabolism. My dose is 0.8ml mixed into a small amount of fruit juice, taken on a mostly empty stomach but not completely fasted. At my weight (75kg) this converts to roughly 1.0-1.2g of GHB equivalent in my system. The onset is about 15-20 minutes and the peak lasts around an hour before a gradual comedown.
The rules I follow without exception: no alcohol at all on GBL days, not even one drink -- the combination is what kills people. I tell at least two friends that I have dosed and what time I took it. I do not redose within two hours minimum, and honestly I try to limit to one dose per night because stacking doses is how people end up unconscious on a dance floor. If I feel like redosing early, I drink water and dance harder instead. I carry my own supply and never share it because I cannot know someone else's tolerance, weight, or what else they have taken.
I know people will say the only safe approach is not to use it at all, and they are not wrong -- the margin for error is genuinely tiny. But people are going to use GBL regardless, so I would rather describe what careful use looks like than pretend abstinence messaging works. If you are new to GBL, start at 0.5ml, have a sober friend with you, and absolutely do not combine it with anything that acts on GABA -- that means no alcohol, no benzodiazepines, no phenibut, no pregabalin.