I have some formulas in my reports, and to prevent divsion by zero I do like this in the expression field:
=IIF(Fields!F1.Value <> 0, Fields!F2.Value/Fields!F1.Va
There has to be a prettier way than this, but this should work:
=IIF(Fields!F1.Value <> 0, Fields!F2.Value / IIF(Fields!F1.Value <> 0, Fields!F1.Value, 42), 0)