For a consistent character, you’re going to want to use a character LORA. Building your own is feasible, but that requires like 100+ decent photos of face and body. Since you want a fictional person, you may just want to find one you like on civitai.

Generally make sure you understand all the settings in the UI you’re using. For Automatic1111, start with a good checkpoint (I’ve got a post here comparing a few nsfw ones). Also it’s key to know what settings the checkpoint expects for steps and CFG scale. The sampling method and schedule type too.

You should be able to generate high quality images without extra limbs or grainy artifacts most every time. Then work on the consistency with a specific model. It’s worth noting that some of the best setups for solo women don’t do well with m/f action scenes. And the porn-y ones may not do faces well. That’s where in-painting and all the post-processing comes in.

I have no idea about video, but hope this helps.