Mix and test your washes before you start. If using Indian ink, use distilled water, as tap water can make the ink separate. For this example, I used a pan of inexpensive black watercolor (a few well-loaded brushfuls) to make a light wash in the mixing well. Payne's Gray also works well, or you might like to try using a sepia or burnt umber wash with a sepia pen.
Mentally 'map out' the areas you want to wash before you begin applying the wash; once your brush hits the paper, try to continue quickly and evenly. This is particularly important if using sketch paper which absorbs the wash and will give you a streaky result if you dither. A fresh, confident approach looks most effective.