I don't do it now; haven't for a while. But if I was doing it, I'd definitely prefer to inject first, so as to induce the stimulant's effects first. I would drink before, but wouldn't prefer it. Afterwards, I would drink just about anytime, but be careful to keep it low, so I don't cause trouble for myself. Later, when I was sure I'd peaked on my stims, I'd dose my benzodiazepines.
I like to experience the pure stimulation before being allowed the option of modifying (lowering it physically, but synergizing with it nicely, mentally) it with my benzos.