By default search results are ordered by the "Updated" field, in descending order. So the most recently updated issue is displayed at the top of the list.
However, you can sort search results by any issue field.
The first option is to specify sorting order in the search request itself. For example:
for: me #Unresolved created: 1900-01 .. 2012-01-12 sort by: Project asc
In this case, search results will be sorted by project name in ascending order (for project names it will be alphabetical order).
You can also sort search results by several parameters. Issues will be sorted by the first parameter, and if it matches, issues will be sorted according to the second parameter.
for: me #Unresolved created: 1900-01 .. 2012-01-12 sort by: Project, Subsystem asc