Often i find some of the maps i make will make there way into reports. This can be either taken up a whole page of A4. Or being 50 percent of the Page or sometimes. 25.
Do people have any page settings they would use
300 DPI is a pretty standard resolution for printing. For a sheet of A4 paper (210 × 297 cm / 8.27 × 11.7 in) that would come to a resolution of 2481 x 3510. For 50% of an A4 page, which is A5 paper (148 × 210 cm / 5.83 × 8.27 in) that would come to a resolution of 1749 x 2481. For 25% of an A4 page, which is A6 paper (105 × 148 cm / 4.13 × 5.83 in) that would come to a resolution of 1239 x 1749. As far as what quality of compression to use for the JPEG, that greatly depends on the specific map, but personally I would not use a quality level below 80%, since fine features will be noticeably blurry. One thing to keep in mind too is if the report will be included in a presentation, in that case you will want to have even higher resolution to work well with a projector.
you may want to look at the Exporting a Map function on ArcGIS Help to start. I have found success in establishing the resolution DPI to be 300 as seen below
You should also take a look at the StackExchange article Is there a way to improve the render quality of ESRI basemaps when exporting a map to PDF or JPG?
and finally, if need be take a look at the ExportToJPEG ArcPy functionality to establish how to increase the quality using the parameters outlined. (The info is from the French ESRI Site so you will need to convert to your language)