One thing I started doing the last time I picked up guitar again, which was about two months ago, was wearing disposable nitrile gloves on my left hand. They're extremely thin and durable, and have minimal impact on dexterity, but allowed me to practice for over an hour a day with no residual pain the next day. It was always possible to practice through the pain on one day, but where I would slip up is skipping a day because my fingers still hurt. (And skipping a day turns into two...) I've still developed calluses, too, but I'm not quite ready to give them up. I'm much happier with my progress than I was any previous time, probably because I never skip a day of practice anymore.

It's not the most eco-friendly thing I've ever done, but I figure it's a pretty small amount of plastic in the grand scheme of things (especially in my line of work).

A little bit of googling tells me that “Nitrile finger cots” exist, that only cover your fingers.

One interesting thing to note is that many people use more force than necessary with their fretting hand. This was certainly true of me. Some hold the guitar neck with some sort of death-grip.

One useful exercise is to fret a note as you normally do, and play it. Then keep picking or plucking that note with gradually less pressure applied by your fretting fingers. At some point, the note will choke and not sound out any more. Then, a little more pressure can be applied to make it sound out again. That minimal level of force is going to be the ideal amount for stamina and to prevent injury. There’s nothing to be gained by pressing harder, in fact you can bend notes slightly sharp by pressing really hard. In many forms of instrument practice, hand tension is often the enemy (especially for faster soloing).

What worked for me was to pick up the guitar every day, and play it for 5 minutes (or more, obviously). No exceptions to the minimum 5 minutes every day rule. I'm pretty good at cowboy chords, barre chords and a bit of blues after around 10 months of this.

And a great way to pick up the guitar every day is to have it ready to go at all times. Keep it outside the bag/case and at arms reach.

And an acoustic rather than an electric (although electrics are great too).