There are 2 main ways of training Runecrafting: The Runespan and Altar Runecrafting at ;;Skilling.
If you are a non-donator, or wish to choose a more AFK method of Runecrafting, use Option 1 (Runespan)
If you are a regular donator or higher, and want the best Runecrafting XP rates, follow Option 2 (;;Skilling)
Option 1: Runespan
To get to Runespan, simply follow EX Tab -> Teleports -> Next Page -> Skilling Locations -> Next Page -> Runecrafting: Runespan
Note 1: Before you can start you must grab some floating essence, near the teleport spot (see yellow square)
Note 2: If you re-click on the creature you're siphoning before it dies, you won't have to wait for the respawn times, getting you faster XP.
1-65: Esslings & Esshounds
Level 1-27: Air Esslings, Earth Esslings, Water Esslings, Fire Esslings
Level 27-44: Cosmic Esshounds
Level 44-54: Nature Esshounds
Level 54-65: Law Esshounds
65-99: Esswraiths
65-77: Death Esswraiths
77-90: Blood Esswraiths
90-99+: Soul Esswraiths
Option 2: Altars at ;;Skilling
(Requires access to pure essence which is sold in the Runes shop at ;;dz - Donator+)
Note 1: Having access to the ;;bank command and keybinding it in Keybind Settings (Press Escape -> Keybind Settings) makes this method much easier.
Note 2: Be sure to make a preset, filling your inventory with essence.
1-65: Air Runes on the Air Altar at ;;Skilling
65-99+: Death Runes on the Death Altar at ;;Skilling
Best of luck on all of your Runecrafting XP gains, and congratulations on any achievements you get.