This is the reason you need to be focused on eliminating Monster. Monster not just provides Essence in large amounts but also other valuable items that you could benefit from. The most effective ones are Gargoyles or Skeletal Wyverns when doing Slayer tasks. Players of higher levels are also able to farm Zulrah boss for drops in the final game and huge amounts pure Essence.
This isn't the only options to obtain Runes as you could also utilize other Runes for your benefit. Temple Trekking minigame offers a large quantity of Essences by putting in a small effort in addition to, when you complete Ardougne Diary, you might be able to get daily runes from Wizard Cromperty.
One of the best values when it comes to the experience you'll gain is through crafting Lava Runes. This process is not very demanding but does need to be fueled by a lot of things. Numerous emeralds are required to create Rings of Duelling as well as Binding Necklaces. They are utilized for quick travel between the bank and the altar. Also, you should unlock the Magic Imbue spell, which allows you to create runes with no need to wear talismans.