Prepare the paper. If you just apply water straight off, the paper will buckle and warp after a bit. Dampen the paper and stretch it out on a flat wooden board. Staple the paper down along the edges.
Pour a small amount of black ink on to the palette. Load your brush with water and mix the water with the ink. Start painting.
If you make a mistake, it's possible to fix it to a certain extent. Grab a dry and clean brush and use it to lift the wet ink out of the area. Though some gray tones will be left, it'll be easier to hide. But don't get too upset by mistakes. You never know when a "mistake" will have an interesting effect.
Experiment with methods of applying the ink. Try laying down undiluted ink before grabbing a fresh brush with lots of water and spreading the ink around. Also experiment with lifting techniques. You can pat an area down with a paper towel to create atmospheric effects. Some artists also like to press balled-up plastic wrap to a wet and inked area. This creates a series of irregular triangles that can have an interesting effect.