Embroidering on sleeves and necklines

If this has been covered somewhere, please let me know! I'm new to the craft and need some advice on how you can properly embroider on a shirt's sleeve and neckline. Any time I put the shirt into the hoop, since there's no tension on all sides, I can't properly get any stitches in. Is there any way to mitigate that so I can embroider all the way to the "end" of the fabric?