Let me suggest some ideas, applications, and resources.
Clip Studio Paint is one of the best drawing applications. It includes “3D models of characters, items, and backgrounds that you could pose and angle to further help as a visual reference.” It can also extract a pose from an image using the Pose Scanner.
From the Materials window, drag and drop a 3D model or character into your scene: All materials, 3D, Body type. Next, pose your character: All Materials, 3D, Pose.
Hands can be posed on a character either by clicking on each individual finger joint or by using the Sub Tool Detail menu, Pose. Manga Perspective allows you to configure a manga-like perspective with the depth emphasized when editing a 3D drawing figure. You can also change the light source, the body shape of the 3D drawing figure, the camera angle, etc.
Alternatively, you could drag and drop one of the four default 3D Characters (there are two school boys and two school girls) into your scene: All materials, 3D, Character.
Procreate is the most powerful and intuitive digital illustration app available for iPad.
Try Alpha Lock and Clipping mask.
First, create your drawing. Then go into the layer menu and select Alpha Lock. From now on, any details you add will stay within the boundaries of your layer. In other words, you won’t color outside the lines or pixels of your original drawing. Clipping mask is quite similar. First, you create your drawing. Second, add a new layer and select “clipping mask.” The base layer will then become a mask and you won’t color outside the lines of your original shape.
Many artists use 3D models for drawing faster and easier: Maya, Character Creator, Poser, and VRoid Studio (it is a free application to create 3D models of humanoid avatars).
Art Pose Apps: MagicPoser is one of the best tools for character posing and art reference. An alternative is ArtPose. It is a fun and artistic app for posing the male and female figure. It allows you to create poses in minutes.
Photo Editing Apps: Photoshop Express (a fun, fast, and easy picture editor for one-touch transformations and photo edits), Adobe Lightroom, and Prisma (a photo editor app that creates photo effects transforming your photos into paintings).
You may want to read our article about Graphics software. Some useful apps: Canva allows users to create social media graphics, presentations, posters, and other visual content. Online photo editors: PicMonkey and Pixlr.