If you wanna tips for Lineage II icons are pretty easy,
First open L2Tool (yeah yeah !)
Open your UTX (icon.utx)
And press "L2 -> UnrealEd"
It will ask you to save UTX somewhere else, Save it as Icon_erteia.utx
Now you will be able to open in Unreal engine 2004 (with Gildor Patch)
And you will see that EACH icon is "32x32" and compressed as "DXT1" so always follow

(This work for any Lineage II texture)
and that allow you to extract texture for port remake, recolor, see ow it work

That how I can do that in C3 :

So to make your icon that pretty simple (if you wanna from ground)
Do any icon as 32x32 TGA or DDS (DXT1)
Import it over Unreal ED with Gildor patch save it (without compresse that not necessary but try both)
Verify you name if that black icon and nothing when you try to move it that one of the following :
Wrong UTX / Icon name (NameOfUtx.NameOfIcon)
Without Gildor tool you can have that error if that not compressed so not readable by L2
Double check compression (if that not DXT1 when you will drag the item that use that icon it will be conrupted

)
If you still have problem feel free to ask

I am not sure if i can give link to L2Tool here but if you need it feel free to pm ^^