Tea staining will only work with natural cloth. Cotton will usually be the choice of fabric you’ll be using. You’ll need a bucket, water, a microwavable cup, bags of dark tea, vinegar or salt, and whatever it is you want to stain. Boil a cup or two of water in the microwave in your microwavable cup. Once boiling, put several tea bags in the water to steep, the amount of bags needed depends on how dark of a stain you want, for lighter stain use three to five bags, for darker stain use as many as you think you’ll need. (I once used twelve bags for a calf length chemise, and yeah, it was overkill.) Fill your bucket with warm water and put your fabric to stain in the water. To get as much of the color from the tea bags as possible, squeeze the wet bags to get the excess water from them, put them back into the water, and repeat. Be careful not to burn your hand, boiling water is quite hot. Pour your tea saturated water into the bucket with your fabric. If you want, put the tea bags into it as well. To get some specks on your fabric, rip open one or two of the tea bags letting the herbs settle into the folds of the fabric. Let it sit for a few hours or even overnight. If the stain isn’t as dark as you like, repeat the process. Once you’ve got the stain you want, dump out the tea leaving your fabric in the bucket, and fill the bucket again with water and add some vinegar or salt. Stir it about, then remove your fabric and either hang dry or stick it in the dryer. The vinegar or salt will help to keep the stain, but as all dyes do, it will fade with time and may need to be repeated.
Here's a great video on some other natural dye methods: