I got my first shot of Pfizer. They automatically scheduled my second appointment for 3 weeks later, but I canceled it, with the plan to reschedule some other time. Two reasons for this: first, while I can't unilaterally impose First Doses First, I can at least impose First Dose First--my second appointment slot was made available for someone else. Second, booster shots for other diseases are typically most effective after a longer interval.
But once vaccine supply catches up with demand, how much longer does it make sense to wait? More long-run effectiveness is good, but the booster is also more valuable while Covid is more prevalent. Eventually, vaccination will drive R below 1, even accounting for the disappearance of masks, distancing, etc. At that point, much of my protection will come from low prevalence and herd immunity rather than personal immunity anyway. There's also the possibility that Covid shots may become an annual thing like flu shots, which would also render this a short-term concern. (Or so I assume--supposing I would end up getting yet another shot later, is the timing of my second shot likely to influence the effectiveness of the third? Do memory B cells use Anki?)
In my case, it's pretty easy to continue taking strong precautions in the meantime, although my wife (who did get her second shot on schedule) will certainly appreciate when we can both go out and do things together.
[Edit: to be clear, my second appointment date had already passed before I posted this. While the other considerations raised in the comments are worth thinking about, I was specifically hoping to get some pointers to information about optimizing my own immune response, probably extrapolating from how vaccines for other diseases work since there hasn't been time to study the Covid vaccines in this much detail.]