Some time saving tips I learned from animators that I’ve been trying to incorporate into comics:
-If you draw or color digitally, make your own textures and kits for things that appear often in your comic- maybe a wood grain or metal texture, or a bunch of generic walls or floors then reuse, transform or modify as needed to save time when drawing new backgrounds or props. This also works for things like piles of books in a background - draw a few then clone them and try to vary them just enough so they don’t look the same.
-reuse drawings when you can - again if you work digitally, if you return to a location or just have a long scene in it, use the same background. If you draw a big establishing shot in high quality you can use certain parts of it for close ups
-before you draw a scene, thumbnail it out then do a pass to eliminate any panels or dialogue not needed to understand the scene. If you reuse backgrounds, see if you can design the scene in a way that doesn’t have you drawing a new background at a different angle every panel. this can help you have less to draw overall, and may also help with the pacing of your comic if you’re prone to adding fillers
-in addition to already mentioned character sheets, if you really like a certain angle or pose you drew, archive it and build a library or add it to your character sheet so you can reference if you have to draw a character or location at that angle again
-the more you understand anatomy and perspective the easier it is to develop personal shortcuts, so studying it before diving in can help save time in the long run
-picking a color pallete for a character or scene before starting can help save time thinking about colors, and unify your colors in the long run
-edited because I just remembered - if you’re having trouble with a scene, physically acting it out or saying the dialogue can help you decide on a pose or how a character should move or react