Set your goals at a reasonable level. About five pounds a week, more or less, is good. If you lose weight more rapidly, you are in danger of many health problems.
This depends on several factors. If you don't have a regular exercise routine and haven't been eating a proper diet then all of a sudden start doing this you will likely see a loss of 2-5 pounds in the first week or two. After that 1-2 pounds weekly is healthy.