This infographic, 20 signs of stress in Dogs, is provided by topdogtips.com click on the link to read, more detailed information.
Some of these signs may also indicate some other underlying health or behavioural issues (same as with any human illness), so keep it all, in context.
Dogs like to know where they are in the scheme of things, they are happy when they have rules, boundaries, routine, exercise, fun, consistency and a space to call their own. The lack or change to any of the above can cause problems for them. All animals speak to us, including dogs, if we as humans, choose to watch, listen and learn.