If you read the instruction manuals for 50's - 60's cars they suggest a 500 to 1,000 mile 'breaking in' period. This means driving normally without revving the engine too hard nor letting it labour at slow speeds, driving gently (not towing tractors?). This gentle driving can be gradually be withdrawn after the breaking in period.
There are all sorts of anecdotes attached to this but revving an unloaded engine is bad because it places huge additional strain on the conrods and pistons. May seem crazy thing to say but if there is no load on the pistons the conrod has more to do yanking them to a halt at the top and bottom of the stroke, because there is less pressure or resistance, so it stretches and bends the rod more than usual. I know a lad who wrecked a really good Yamaha R6 racing bike engine just blipping the throttle, put a rod right through the side.
The original Austin Seven engine crank only had two bearings, a roller bearing at the front and a double row ball bearing at the back, when #'s 2 and 3 pistons rattled on the head it was time to change up. They very rarely broke the crank... Austin then decided to add a third bearing in the centre of the crank. Those engines didn't rev as well and they broke the cranks, which adds weigh to the argument that if it ain't broke, don't fix it.
As for the pistons and rings, the rings need pressure to cause them to seal, if they are just flapping about in their groove they aren't sealing very well.
My son showed me a video of really good demonstration by James May of ejecting a piston from a slightly slack bore, compared with ejecting a piston from a perfect bore. The difference was significant. They used compressed air and something like a large air gun. It may even be on U-Tube somewhere, in fact that's probably where he found it...
For a normal 'old' road car I don't think there is any need to get too hung up about warming the oil and stuff. We used to heat the oil (Castrol 'R') before we went on rallies in winter but I think it was more of an adventure rather than from necessity. The historic racing lads still do it in cold weather because cold Castrol 'R' is a bit like syrup! Modern multigrade oil is a different thing altogether.
The only other thing I can say is avoid driving up big hills with a cold engine and change the oil regularly.
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