The stem stitch is fantastic for vines, branches, flowers and outlines. It also looks great for text, but you've gotta be careful with sharp corners.
A stem stitch is similar to a backstitch, but instead of linking stitches at the ends, you're going to instead bring the needle up for the next stitch right next to the last stitch.
Make a small stitch about the length of a grain of rice. Bring the needle back up through the fabric on the right or left side of the previous stitch, fairly close to the end of that stitch as shown in the second photo. Keep starting your new stitches on the same side of the stitches you're already put down.
This stitch is easiest to practice with lines drawn - when you try it without lines it can be tricky to know where each stitch should end.