Satin stitch is a very useful stitch for filling areas and can give a lovely, bold effect.
Firstly, determine the area that you want to fill with satin stitch. I am using a basic leaf shape to demonstrate.
Start sewing from the middle and work your way outwards. This is done to keep the stitches as straight and even as possible. It can be useful to draw in extra lines in the direction that you want to make your stitches as extra guidelines. With practice this won't always be necessary though. Bring the needle up through the fabric in the place where you want your first stitch to start, leaving a tail at the back to secure in as you sew, (as shown in 'Getting started').
Bring the needle back down through the fabric where you want the stitch to end, as shown below.
Remembering to keep a finger on the tail at the back of the work so that it doesn't pull through, gently pull the thread until the long stitch lies flat against the fabric. It should not be loose, but also doesn't want to be too tight as this will result in the fabric puckering. It is recommended that you mount your fabric in an embroidery hoop or frame when sewing this stitch in particular as it really helps keeping the fabric taut (like the skin of a drum) to make nice, even stitches.
For the next stitch, bring your needle up through the fabric just alongside your original starting point, following the line of your pattern, as shown in the picture below. There should not be a gap between, but also, the needle should not be coming up underneath the first thread.
Push the needle back down through the fabric so that the second stitch runs parallel to your first stitch. Again, position the needle so that it does not take the thread underneath the first stitch, but also does not leave a big gap.
Repeat this process to fill one side of your area, gradually adapting the length of your stitches to fit your chosen pattern shape.
Continue to stitch in the same way to fill the other side of your pattern, keeping the stitches as parallel as possible so that they run straight alongside each other.
Your finished piece should lie flat against the fabric and the fabric should not show signs of wrinkling or pulling in any direction.