I'm writing this journal to help artists who are searching for exposure.
Most of your art's first impressions are going to come from thumbnails. When you submit to a group and that groups gets 20 or 50 submissions a day your thumbnail is going to make all the difference.
When I'm going through my messages I often come across a lot of practically white thumbnails, which are usually pencil sketches. With so many messages, when I see these and I can't discern what they are I have to judge the picture by the title alone and if the title isn't really interesting I likely will delete the message from my inbox without seeing what it really was. I'm not suggesting to stop uploading sketches, but I am suggesting to make the lines clear. If this is a scan of a real sketch then go to an image editor and set the contrast very high. If this is a digital sketch then make the sketch with thick enough lines, don't make the lines pale or transparent.
I'm sure I'm not the only one deleting white thumbnails from my inbox.