Step 1 Ask yourself some questions,
What place/time are you going for? This will inform what style you will use.
What is the stitching on? Clothes, a pouch, or a cushion will influence the shape the stitching needs to fill and thus the motifs chosen.
How much area do you need to cover? This will also influence what motifs are chosen.
Are you going to want to wash it? This may inform the materials used.
How much money do you want to spend? This will also affect the materials choice.
What place/time are you going for? This will inform what style you will use.
What is the stitching on? Clothes, a pouch, or a cushion will influence the shape the stitching needs to fill and thus the motifs chosen.
How much area do you need to cover? This will also influence what motifs are chosen.
Are you going to want to wash it? This may inform the materials used.
How much money do you want to spend? This will also affect the materials choice.
Step 2 Look at the art of the place/time you have chosen
The same art style and motifs were used in other art forms. Jewelry and architecture can give general shapes that were popular. Carvings and manuscripts can provide the look feel of the figures and the art style. In later period, portraits show embroidery.
The exact same figures from some manuscripts have been copied in stitching. Late period had published patterns for the home stitcher to copy from. Straight up copy as much as you want from period sources.
The same art style and motifs were used in other art forms. Jewelry and architecture can give general shapes that were popular. Carvings and manuscripts can provide the look feel of the figures and the art style. In later period, portraits show embroidery.
The exact same figures from some manuscripts have been copied in stitching. Late period had published patterns for the home stitcher to copy from. Straight up copy as much as you want from period sources.
Step 3 Bring it together
Once you have selected the elements you want to include, arrange them according to the style you have chosen, to fit the space you need to cover and create the final pattern through tracing or redrawing.
Use your local illuminator to draw your pattern, if drawing is not an art you are comfortable with. This was absolutely a period practice: Stitchers stitched, Draughtsmen drew the patterns.
Once you have selected the elements you want to include, arrange them according to the style you have chosen, to fit the space you need to cover and create the final pattern through tracing or redrawing.
Use your local illuminator to draw your pattern, if drawing is not an art you are comfortable with. This was absolutely a period practice: Stitchers stitched, Draughtsmen drew the patterns.
Step 4 Final details
Now that you have your pattern go back to your step 1 questions and choose your materials, colours and implementation plan.
If the embroidery will cover the entire area of the shape you are stitching, the ground cloth doesn't really matter (unless you're entering a competition). It is sometimes easier to stitch on a cotton or linen ground and then applique the stitching to the article, particularly tunics and the like. So long as it supports the stitching, a lighter weight fabric can be a perfectly suitable ground fabric without the expense of the fancy high-count even weave linen marketed to stitchers. If the embroidery will be open, the applique method is probably not the effect you're going for and you'll want a "pretty" ground fabric for various values of pretty.
Your floss should be able to stand up to the technique you want to use. Some flosses will fracture when pulled through a dense weave. Know your floss, experiment with your chosen ground fabric, make adjustments. Alter your design if needed.
Now that you have your pattern go back to your step 1 questions and choose your materials, colours and implementation plan.
If the embroidery will cover the entire area of the shape you are stitching, the ground cloth doesn't really matter (unless you're entering a competition). It is sometimes easier to stitch on a cotton or linen ground and then applique the stitching to the article, particularly tunics and the like. So long as it supports the stitching, a lighter weight fabric can be a perfectly suitable ground fabric without the expense of the fancy high-count even weave linen marketed to stitchers. If the embroidery will be open, the applique method is probably not the effect you're going for and you'll want a "pretty" ground fabric for various values of pretty.
Your floss should be able to stand up to the technique you want to use. Some flosses will fracture when pulled through a dense weave. Know your floss, experiment with your chosen ground fabric, make adjustments. Alter your design if needed.