Anor Londo is one of the smallest areas in the game, consisting of the small areas outside the building and the main hall. If you played Dark Souls 2 you may be familiar with this area, but it is very easy to navigate even without this knowledge.
Head up the stairs until a Silver Knight charges forward and then back up to fight it, as another Silver Knight will come up behind it. Grab the Large Soul of a Weary Warrior to the left of the stairs and then enter the arch on the right to encounter another Silver Knight, collecting the Soul of a Crestfallen Knight from the bottom of the stairs after defeating it.
You can now return to the main staircase and enter the arch on the other side to find a entrance to the building with the Giant’s Coal .
The stairs lead to the upper level of the main hall, where you’ll encounter a number of Deacons of the Deep and Writhing Rotten Flesh.
Make your way down the stairs and clear out the majority of the lower level, grabbing an Estus Shard from a chest at the base of the stairs and the Moonlight Arrows from the opposite staircase, and then head toward the left side of the main doors.
A lever here will open the main gates, but approaching it will also cause the Deep Accursed to drop down.
Make sure to pull the lever before you engage the accursed, as it will make returning to the main hall easier if you die, and once the doors are open back out toward the main staircase. The slant in the stairs will help you avoid any attacks from the Deep Accursed, as they often go over your head or won’t land directly on you, and this should make defeating it for the Aldrich’s Ruby much easier.
You can now rest at the bonfire and simply rush through the main hall when you want to take on Aldrich.