When looking for flow, you would want something that looks like it flows or is flowing, or has some sort of movement like the focal or whatever is moving to or towards something.
When looking for depth, you want to be able to see far in the sig, or you want something to pop out and you can see far in the sig. If you see something like a solid color, or a color with lines over it with no effects, that would be flat, and things of the like. Good depth is when you can see far and it seems like you are actually there looking at what the depth has.
Focal Attraction, more commonly known as the focal, would be the focus of the sig, or where you want yours and others' eyes to look at first right when you or they see the sig. If the sig is too bright or has too much effects/FX, noise, or something distracting, the focal will be lost. Also having one focal is the best thing, more than one will be confusing.
Blending is something that looks like it is in the sig, not like somone slapped something on, or just put the focal there and did nothing to it. Though, this is usually necessary for only renders.
Lighting sources are important to give the sig a more sense of it's actually real or it's happening. Though when making a lighting source, it is best to have it be on the side where the light is coming from on the focal. Like if it looks like the light is coming from the right side of the render/stock, make the lighting source there. Usually make the lighting source near the head of the focal, if it is a living thing as it attracts more attention.
Negative Space is where there is like an empty sort of space in sigs/large arts, which every sig needs. If you have too little, the sig is too noisy and it'd be difficult to work with the focal. Though, if you have too much negative space, you might end up having a flat, boring signature. It's good to balance the neg space out.
'Tis all for now, kthxbai
