Here is the "official" word, take it or leave it, but no whining if you ignore it and have trouble.
1. Here is the number on thing to know about breaking with the Bullet. HEAT is the enemy. I am not going to tell you to go only so fast in any given gear as the reason for that is to protect you from yourself. A 500cc air cooled cylinder is a BIG cylinder and will produce a lot of heat. A new engine has all sort of rough surfaces rubbing against each other. ( At the microscopic level). This produces more heat than later when these surfaces are "broken in" At a speed of say 50 or less the Enfield can normally dissapate the heat that it generates, but at higher speeds for a period of time it cannot. This can lead to a seized piston (forget your warranty it is your fault pure and simple), and other forms of heat damage. Of course the outside temperature etc. plays into this. Drive your bike using common sense!!. Take it extremely easy until you have 300-500 miles on it. Around 500 miles get the initial service (This is very important). Between 500 -1,500 take it easy but you can push the envelope harder, Can you run it up to 60, sure but not for any extended period of time at all. After 1,500 miles the engine is a different engine than it was new and can run at faster speeds. NEVER lug the engine (even broken in), vary the speed, this allows oil to get thrown under the piston to the piston pin and helps the rings. Once the bike is broken in don't ever forget that it was designed to be a 55-60mph machine. It will go faster, but nothing can be driven at full throttle (or close to it) for long.
2. The rings need to seat. There are as many tales about how to do this as there are brands of motorcycles. Most have some basis in fact in the old days. For example, Ford used to "age harden" blocks, they would cast a block and then throw it out in the elements for a couple of years to harden. This was the state of the art for cast iron. Over time those blocks became very hard and it sometimes was difficult to break in the rings. An old garage trick was to throw some very fine grit into the carb to to the work fast. ( I have seen this myself) In this day and age this is now very bad advice. Metallurgy is such that rings will break in on their own with no special treatment. There is really nothing you can do that will prevent this from happening so don't worry about it. Very modern rebuilding manuals even say not to hone a cylinder any more because the hazard of honing grit (even with the best of cleaned cylinder walls) is worse than a longer ring break in period.