I have helped many clients get thru separation anxiety issues with their dogs, and it is different every single time. Some dogs whimper a little and settle after a few minutes, a minor case like this can sometimes be addressed with something as simple as a kong stuffed with treats. More severe cases require a much more in depth solution, and I strongly suggest seeking out a trainer or behavior consultant to help you develop a plan. Some keys to success are focusing on positivity, taking your time, and exercise. Any negative influence will only increase the dogs anxiety when you leave, baby steps with short periods of separation build to longer ones as the dog learns and becomes comfortable, and exercise your dog and drain their energy before you try to leave them alone (this is to prevent the destruction of your property as much as it is for the dogs benefit). The link below is a great article about separation anxiety posted on the ASPCA website.

Source: http://www.aspca.org/pet-care/dog-care/common-dog-behavior-issues/separation-anxiety