Are you just animating the base skeleton, or do you use any automation?
What types of animations, long, loops, partial (mixed together to make more complex loops)?
I find the mistake a lot of new animators make is that they try to animate ONLY the base skeleton, not realizing that is probably the worst way to animate. That is like trying to draw characters straight to paper, not using any techniques to make your work easier or more reliable.
One technique that I live by to solve every problem is: abstraction. Abstraction is to break down a problem into its key simple parts. For example, a walking animation. What you can do is add more bones (or another skeleton), and use these bones to automate some key behaviors. One behavior that is very important, a key thing in walking, is balance. When you take a step, your hip shoots out to the side, your spine makes a curve, and you actually move the center of the body so that it is balanced over the foot (it helps to have your character start out in a standing pose). What you can do is use either use the copy rotation modifier on the bones of the character skeleton, or I prefere to use the more complex Transform modifier, and what you want to do is first get a rough idea of how you want your character posed (ie rotate each bone, get an idea of how much each bone should be rotate, with respect to their local/parent local cordinate system). After you have an idea of want to do, you determine or create a control bone that will represent this abstraction (ie I like to move a bone 1ft to the left of the character to represent the character shifting their weight to the left), and then for each bone of the skeleton that you need to move to get the shape you want, you add a modifier and adjust the numbers so that you are able to generate the pose you wanted using the control bone. You then repeat this proces for other different aspects of the animation (ie twisting the bodie, used for energy efficientcy while walking). The only issue is that you need to understand the mechanics of locomotion of the human body, which is the key to figuring out how to break down an animation into it's basic parts. You can then add another layer of complexity, using control bones to control other control bones. ie if you make custom shape keys for the breasts so that they look correct for when they go up down left right, you can use one bone to control the boob and the left right keyframes, and another bone for up down stuff, and then a boob bone that controls the previous control bones, so that you can use one boob bone to move the boob in all directions. Similarly I use such multi layer complexity to automate a lot of animations, such as walking, and deing effects like, the way the body shifts it weight to turn or make quick turns.
Having bones that control various abstract ideas about an animation (weight distribution, breathing, looking down, facerig/moaning effects) makes it easy not only to make looping animations, but to make longer animations where you can add in new effects later on without having to make any modifications to your animation. IE you can make a fuck up and down control pose. you can make a lean forward backwards control pose, you can then latter add on a rotate the hip side to side, forward backwards, so that you can first animate the fuck control bone, and then part way through the animation you can animate the hip rotate bones so that it looks like the character is gyrating their hips to make the sex more pleasurable.
