At a glance creative process may appear to be completely spontaneous and chaotic. In fact, sometimes it's better this way, especially when you're not bound by any kind of time limits. In other instances though it's much better to get it organized. Organizing your workflow in clear stages will help you build up a steady working habit that eventually will save you a lot of time and nerves and will help you define the most crucial moments of creative process.
Idea & Sketch
Everything starts with it, and arguably this is one of the most challenging aspects of all. Getting original idea of an artwork may require some additional research done. First of all, define your subject. Next define things you want to accentuate your attention on. After that move on to using Internet to find out information relevant to the subject. For instance, you want to make Hades/Persephone inspired artwork. What sort of info would be relevant? Original source, i.e. myth. Classical artworks. Various critical articles on the symbolism. Last but not least, media depictions of these personages. When you have compiled enough information, proceed with a rough sketch or series of sketches and pick the one that stands out most.
Materials, Styles, Tools
Decide on style. Is it going to be realistic, semi-realistic, abstract, etc? Are you going for digital media or for traditional look? Are you going to use specific colors to achieve special effects? When done with your idea, start gathering working material. References, textures, etc. There's plenty of reference sites, moreover you can always check DA's resource section. Deciding on textures is more tricky so it's best to gather as many of those you deem suitable as you can. Think about custom tools that can help you speed up your process, such as fabric texture brushes for example.
Working & Adjusting
It's fairly normal to deviate from original idea during the working process itself. You may have a brainwave and come up with a different better solution. Don't force yourself to do everything in a single sweep. It's normal to have blocks when you can't seem to find the right approach. That is why it is important to take breaks. Stand up, have a cup of coffee, get some air. Looking at your artwork with a fresh eye may help you identify your problem. If you are working for 12 hours straight and it still doesn't look good, then lets admit it, you're probably doing it wrong. Think about what causes the issue - chances are you're not alone in that. If so, it's easier to find tips and tutorials online which may help you do it right. Why invent the bicycle when you can draw on shared experience.
By and large, the artwork is done. Can it be better? It's time your experimented with additional edits. Check on details, paint in some more tiny features. Change color, adjust brightness, add texture. Glitter? Sparkles? Bokeh? Lens flares? Frame? You decide.