Greetings,
looking for and identifying varroa on a sticky board is somewhat like
looking for nosema under a microscope: difficult to identify the first one
but afterwards it's much easier. And of course, if it's not there, then it
takes a lot longer to check the sticky board. Here in Quebec we use the
Phero Tech sticky board which has a very even coating of a good adhesive. I
was lucky to have my first experience with varroa mites in 1989 in the
Philippines, we had lots!  I use a magnifying glass (from a dollar store)
and keep it stationery while l move the board. This way the "mites" are
always in focus. We live the boards in for no longer than 3 days to avoid
debris buildup.
Peter