I don't know exactly what you are asking but I will do my best to explain.
I have written some thoughts on similar subject before.
Also I am sorry, I do not know of "methods" but I hope this is informative.
To start, everything probably begins with the character design.
Many characters follow logical derivations from human anatomy exact or similar.
To my knowledge, anatomy is also not necessarily locked onto the human figure.
Anatomy I think is the ability to consistently use/manipulate forms and the proportions of forms.
Tagging along but separate is the knowledge of all standard forms/proportions for real human figure.
The reasoning is that specifications of forms will vary for characters, but the skills to use them are always the same.
From my observation, much differences of "style" are due to some new sets of specifications but most of it being derivative.
Derivatives from other "styles" but many are from real world anatomy like humans.
Some character designers actually have to adapt comic designs so that they are better for animating.
However, many characters do in fact closely follow the anatomical proportions/forms taught.
Many books teach these like famous illustrator Andrew Loomis.
Animators can draw upon this knowledge to draw character repeatedly since they are locked in character design.
They have memorized this information or analyze the character sheets for new ones.
Akko is six heads tall. Her waist is half a head. Her sleeve widths are one head at max. Her arms are the same width as her neck. Two heads down from the top is the end of the hoodie from the neck. Three heads down from the top is the crotch and where the skirt has a little indent on the side. 1/4 head down from there is the end of the robes. Akko's head is a circle plus 1/8 of the circle and with a normal mouth open, her chin moves down by another 1/8 of that circle. At the top of that circle her bangs emerge. 1.5 heads from the ground is the side of the boots. One neck width from the neck is the inner part of the hoodie on the shoulders and another neck width from there is the outer part of the hoodie from the shoulders. Half a neck width away from the neck is the inner part of the robe on the shoulders. 1/4 a neck away from the neck is the inner part of the collar on the shoulders. 1.5 heads from the top should be where the plane where the ends of the hoodie resides on the side of the shoulders. Half of the head is where her browline is. 1/4 of her head is where the bottom of her nose is. 1/8 of her head is where the bottom of her lip is. Where the top of her ear inserts into the head is the plane of her eye and the bottom inserts into the plane where her mouth is. 2.5 heads down is where the bottom of where the top part of the belt resides and 1/4 a head down from there is where the bottom of the bottom part of the belt resides. The belt buckle is square with 1/4 head. Wand is 3/4 a head.
Whether this this accurate I don't know, I would have to ask Studio Trigger or Yoh Yoshinari.
It is however is knowledge of the character that one can modify in their head as one draws the character more.
I think trusting the eyes to look for consistency without anchor is not good enough.
They can play tricks and minute changes between frames can add up into terrible results.
On top of that, one must also quickly animate the cut in time.
So to me, drawing with knowledge first is more reliable than the eye.
It is said that animators are very observant, this might be reason why.
Not only following the landmarks/proportions taught in anatomy books, but identifying character specific ones like the clothes.
Additionally by analyzing how the character is designed, one can extrapolate many other things.
Head and body features can give information about age of character and vice versa.
Western character design is the same except things are much more explicit to my understanding.
Again this is what I analyze from the sheets beyond what is stated.
The body is about same width as the head. The shape of the head is almost identical to the shape of the torso down to the feet. The torso/pelvis is also based on the same or close to the same circle as the head. I believe the neck is one third of the head's width and inserts into the head at the same vertical plane as the eyes. The arms without the hands seem the same length as the head. The legs without the feet seem the same length as the head.
This is from POWER PLANT NO. 33 (Animator Expo #11)
Not exactly a model sheet but it kind of reveals how proportion is considered.
Also, if one takes out an anatomy book that includes information of landmarks, one will find a similarities.
Regarding likeness of the heads, that really is again much knowledge of analyzing the character or using previous knowledge.
Features themselves like hair and eyes have a certain shape, silhouette, and/or form.
Heads have a certain proportion for the features depending on style, age, and/or etc.
The information for the character is all in the model sheet by analyzing beyond the level of, "Does this look the same?"
It is knowing what the exactly thing is being drawing and accounting for that in the entirety.
Sizes, anatomy, proportions, line thicknesses, details, forms, angles, and etc.
On top of that knowing these things means nothing if one cannot manipulate it in space.
Strong knowledge of perspective is required to understand how forms change in response to perspective.
Draftsmanship is practically a prerequisite as a result for creating good animation.
The important thing is not construction for the sake of construction, but for understanding.
The more knowledge one has the less construction is needed because one already knows what one wants to draw.
For best animators, I think they naturally analyze in addition to having strong draftsmanship to use the information.
A good artist Vilppu says, "No rules, only tools" and also to not copy but analyze.
Anyways, I am self-taught so I recommend asking a professional animator or someone studying animation in school instead.
Sorry if what I wrote is not very practical, they probably have better knowledge.
This is just theory and experience of my own so I don't know if it will be useful to others and it can also be incorrect.
Thank you for your time if you read everything.