I’m going to be lazy and link to the post I did where I described how I first got into this: #msg48526.
That has pretty much everything I have on this, including the ritual I’ve used a lot and the idea about painting the eyes last.
What’s probably more important than the specifics, is that I found a set of ritual cats that seemed to me to be effective, and stuck with that - so if you have any idea in your head of how this should work, if, for example, you were to write a short story about a magician doing this, that’s probably a useful way to find what will be most effective for you?
I had to seriously make up so much of my earliest stuff, and almost all of it has carried through to now, some 25 years on!
Also, can you anchor more than one spirit to a single idol?
I wouldn’t do that myself, though it’s probably possible, but it’s nicer IMO to make the image as nicely specific to that being as possible, so that would rule out giving it to another spirit to share.
I wouldn’t like it if someone asked me to a dinner party and then insisted I share my seat - and plate! - with another guest, in fact I’d be downright pissy.
Belial is notoriously angered if you give him something, then try to take it back or do anything HE hasn’t approved with it, when I did the artwork for him in the Evocation Art thread he ROARED at me at one point, when I was doing the sigil drawing and wanted to change something - he was very determined it should look a specific way!
So unless you have some kind of compelling reason, I personally wouldn’t advise doing this, the risk of it causing problems is far too high.