Fuller figures are drawn poorly for the same reason feet and backs are: most artists have never practised them, so a shorthand fills in. The shorthand usually consists of adding uniform width to a standard construction, which produces a figure that reads as inflated rather than as a body with more soft tissue on the same skeleton.
The corrections are structural and they are the same principles that apply to every figure. Nothing here is a special technique; it is ordinary construction applied to a case that is usually skipped.
The skeleton does not change
Ribcage, pelvis, and the lengths of the limbs behave as they always do, and soft tissue sits on top of them. That means the landmarks are still there, and still findable: the collarbones, the point of the shoulder, the wrist, the ankle, the knee. Locating them first prevents the inflated look immediately.
Where soft tissue is deeper, landmarks appear as dimples rather than as projections, since the surface dips toward the bone rather than rising over it. Drawing them as dimples is one of those small observations that changes a drawing entirely.
Contours are overlapping forms
The outline of a fuller figure is not one smooth curve. It is a series of separate soft masses that overlap, each with its own edge, and the places where one ends and another begins are the most informative parts of the drawing. A single continuous contour reads as a balloon.
Drawing the overlaps explicitly, even faintly, gives the form structure and depth. This is the same cross-contour thinking described in the piece on drawing soft structure, and it matters more here because there is more soft tissue to describe.
Weight compresses against things
Soft tissue spreads where it rests. Sitting, leaning and lying all produce visible flattening and displacement against the supporting surface, and drawing a figure whose outline is identical whether standing or seated is the commonest error after the balloon contour.
The same applies between parts of the body: an arm against a side, a thigh against a thigh. These contacts deform both, which is the contact logic in the piece on two bodies in contact, applied within a single figure.
Clothing tells you most of it
Fabric over a fuller figure produces different tension patterns: more places where it is stretched, different hang, creases forming where flesh meets flesh. Drawing those correctly describes the body underneath more precisely than the bare outline does, which is the argument in the piece on how fabric describes a body.
It also solves the design problem of distinguishing characters, since fit and how a garment sits carries a great deal of information about both body and personality.
Proportion is not uniform
Soft tissue does not distribute evenly, and drawing it as if it did produces a generic figure that resembles nobody. Real distribution varies enormously between individuals, and choosing a specific pattern for a specific character is what makes her a person rather than a category.
This is the particularity argument from the piece on the default body. Variation among fuller figures matters just as much as variation between them and everyone else.
Practising what you have avoided
The route through is the same as for any avoided subject: draw them specifically, from reference, with the landmarks plotted first. Twenty drawings will remove the shorthand, and the improvement transfers to every figure, since the underlying observation is about soft tissue generally.
It also widens what a cast can contain without the drawing quality dropping, which is the practical reason to do it rather than a matter of principle.
Reference is the practical bottleneck, since libraries of drawing reference have historically been narrow. That has improved considerably, and photographing willing friends, using life drawing sessions with varied models, or paying for reference from services that offer a real range are all straightforward routes. The rights and likeness considerations are the ordinary ones described in the notes on using reference responsibly.
Drawing a fuller figure properly
Plot the landmarks first, draw overlapping masses rather than one contour, show compression against surfaces and between parts, use clothing tension to describe the form, and choose a specific distribution for each character rather than a generic one.
Characters here are fictional and unmistakably adult, as set out in the reader agreement.