Elden Ring bosses are tough. they're big, fast, and many of them have multiple phases. They're the cause of many a broken controller, but the sense of pride on offer when you finally beat them down is priceless. You do also get a Rune reward for beating them though, so that's sort of like a price.
Reddit user Not_Quite_Vertical shared a map that shows both the location and Rune reward for every boss in Elden Ring. You can use it as a sort of intended route for how and when to take on the various bosses, as the ones that give more Runes tend to be the ones of higher level and difficulty.
The rewards for defeating the bosses range from just 800 Runes to 480,000 - that's enough for an entire level once you're at the end-game. It would be tough to kill all these bosses in ascending order of Rune reward as many of them are scattered far and wide across the map. Mini-bosses in particular offer varied rewards even into the mid and late-game.
Still, combining this with the level scaling information that was uncovered last week gives a rough idea of the order the game is meant to be played in. Obviously, as with many open world games, you're free to tackle the game in what ever way you want, but it could be fun to go through as close to the intended path as possible.
While Runes are primarily used to level up, one player has shown us that it's possible to beat one of the toughest bosses in the game without taking any damage, and at Rune level one. Still, it doesn't hurt to use them to level up your equipment and Spirit Ashes.