Hi spencerokada,
There are other ways, but the main idea is to connect each and every point to one or more joints, so the movement of the points becomes more natural. With the joints in play, the angle among them will give even more options via XPresso. Especially for an arm, Muscle Objects might lead to a more realistic appearance, and those are driven typically by joints.
As vytas_rauckis said, Pose Morph is the next option. Other options could be just a Spline with a Spline Wrap, or just a simple Bend Deformer, perhaps a Mesh Deformer, well anything that can move points in an wanted order.
Typically an object/character is posed during modeling in a neutral pose, as it is called T-Pose for bi-ped (and two arm) figures. It follows the idea to keep all points as separated from each other as possible and in a way that allows for a position to see all points, roughly said. The opposite would be a figure sitting in a lotus formation and with the forearms on the legs. That will cause some extra work to differentiate for any animation work, and a standing stretch with arms in the air will perhaps show some weird deformations. The common T-Pose is even a requirement in many, more or less, automated rigging options, see the Maximo series here on Cineversity for more information.
https://www.cineversity.com/vidplaylist/mixamo_to_cinema_4d_character_workflow/mixamo_to_cinema_4d_character_workflow_rig_characters_export_with_mixamo
All the best