There are several ways to get Runes in Elden Ring as fast as possible by doing possible Main Quests and Side Quest.
The first thing you have to do is to mark the site of grace and meet the White-Faced Varré NPC and talk to him and he will ask you to do defeat the Godrick the Grafted.
After defeating the boss come back to the same place where you meet the White-Faced Varré NPC. When you arrive at the place there will be a message for you. The message is about to go [Rose Church].
Make your way to the Rose Church by approaching the site of grace near the Temple Quarter. Whenever you spawn at the Temple Quarter Grace go southeast from the church kill side enemies in your way and you will reach the church. For the first time, you will reach there you will same White-Faced Varré NPC who will give you Bloody Fingers. Now you have to use three of them and invade other people’s worlds. If you win or lose it doesn’t matter. Just talk to him again and he will give you a Handkerchief that you have to soak with a maiden’s blood. For that, you have to go to the Church of Inhibition.
After reaching the place you will find a dead maiden. Interact with her and soak your cloth with blood.
Go back to the church and interact with the White-Faced Varré NPC again and he is going to give you an item named [Pureblood Knight’s Medal].
Use the item and you will be teleported to a Place named Mohgwyn Palace. Use the stairs and reach the site the site grace through bloody lakes in your way. One thing to be alerted to is that don’t interact with long Flutes because they will kill you instantly. Once you reach the site of grace equip the items like Gold-Pickled Fowl Foot which will increase your Runes by 20 percent. Also, equip your Bow and arrows so you can little enemies by far.
After equipping these things you will see a bloody lake downwards there you will see a bird. Stay at the corner of the hill target the bird and shoot. After shooting stay at the same spot still because if you move he will back up and probably kill you. He will fall and die.
After killing the bird you will get 11000 Runes per kill. After killing the birds use the site of grace to reset the enemies and kill them. This is how you can get Runes as fast as possible. This is the best Rune Farm to get 3 million Runes.