There is a diference between "breaking in" an engine & "running in" an engine. Give it hell, or baby it? Probably a bit in-between, read on.

Breaking in is the first half to one hour or so of running & is usually done in the workshop. A very light oil is usually used without any friction modifiers. This process involves running the engine at an engine speed of something above 1,500 rpm & many would say to use about 1,750 as a minimum. This is to ensure that the cam stays lubed [splash fed on the lobes] & that nothing gets loaded up too much. It also keeps the fan spinning & that helps to keep the temp under control. Keep a good eye on the temp as nothing kills engines faster than heat. Blip the throttle occasionally to vary the revs, but do not load the engine up. Do not race the engine. Blip to about 4,000 rpm max.

Once you are happy with this break in period, i suggest that the oil & filter be changed as this is the time when the greatest amount of metal particles will have been liberated from the freshly machined surfaces, & in my view, the price of the consumables is cheap insurance. Use the grade of oil that is recomended in your owners manual. No manual? Pretty much any manual from any passenger car will give the same sort of info. I think a tune up is in order. Check tappet clearances, points [if fitted], & timing as best as possible. In a new engine, it doesn't take much for these settings to settle in & change from when you set them to, an hour ago.

Running in.
Once again, the manual is a good reference, but basicly, you want to minimise "local" heat buildup. By this i mean that some of the parts inside your engine can get pretty tight once the engine has warmed up, & while the coolant temp is good, some parts inside can get a lot hotter than we would like. Since this heat buildup can rise almost exponentially with load & speed, it's a good idea to keep the pressure, & revs, down a bit for a little while. Once you have a little mileage on it, a few short full throttle bursts will be helpfull. I do not suggest going over 66% of full available revs just yet. This full throttle stuff from about 2,000 rpm puts maximum gas pressure behind the top rings & helps to seat the rings properly, but don't over rev it. Keep the idle revs somewhere near 1000, or whatever it takes to smooth out the cam a bit. In fact, you may have some break-in, & running-in recomendations with your cam.
A good indication of engine tightness is the speed with which it stops when switched off. If it stops in just a few rotations from about 1000rpm, you got a tight one. Tight equals heat. Heat is bad. As the mileage mounts up, you will notice that it doesn't come to a stop quite so quickly. Just keep an eye on this stopping thing as It is interesting to observe over time how this settles down.

I guess that at about 1,000 miles, i like to dump the oil & filter again, check the tune up settings, & bring the idle back a little. Like the book says, increase maximum engine speed & load as the miles roll on, but i personally do not like prolonged full power runs untill somewhere between 3,000, to 5,000 miles.

I'm sure that there are many who would flog the bejesus out of it right out of the shop door, but when i'm paying for it, i take care of it during the first days & weeks of life, as an engine siezure just ruins your whole day. Even if it just "picks up" in the bore [scoring, the first signs of piston siezure, not usually noticeable at full power] it damages rings, pistons & bore, & that shortens engine life, reduces power, & increases your costs. I like to check head tension again [cold] at somewhere between 5,000 & 10,000 miles. I know that mono-torque gaskets do not need checking, but i trust no-one, particularly advertising men. I check mine again about every 30,000 to 50,000 miles [depending on degree of laziness] as head gasket failures, particularly at the rear where it gets a bit hot, are not unknown. A half hour with a torque wrench at tappet check time can save a lot of inconvenience.

Conservative?.... Me?... Bloody oath i am. I got very good life from my 1200 GX engine, twice, & i gave it a damn good workout during it's time on the road, but i built the engine a little on the tight side both times & took things gently for a while. It all worked for me. Just watch that heat, & change the oil & filter a few times early on to get rid of the metal particles. A magnetic drain plug, or even a magnet in the pan is never a bad idea. Any piece of metal in the oil, no matter how small, that is taken out of circulation, is a piece that can do no harm.