Check the detailed explanations section on the pinned discussion: 'Shiny Configuration & Admin Commands'

the settings you'll probably want to look at are:
SpawnIntervalMin and SpawnIntervalMax
MaxNumShinies
NumSearchLoops

Make sure you have the tracker enabled and use the admin spawn code to get it. This should show you all live shinies.

Also if you are running in Singleplayer, (full explanation in pinned FAQ discussion) you will need to add the '-PreventHibernation' launch option