Hgb <7.0: give 1-2 units of packed red blood cells (although there are certain conditions in which patients should be transfused when Hgb <8.0)
Plts <10,000 or plts <50,000 and the pt is actively bleeding: give 5-10 units of platelets. In pts with heme malignancies with abnormal CBCs, this threshold still applies.
When pts have DIC and low fibrinogen (<80-100 mg/dl): give 5 bags of cryoprecipitate (in addition to fibrinogen, also contains assorted things like von Willebrand factor, factor VIII, factor XIII).
When pts with liver disease are bleeding, need emergent warfarin reversal, are actively bleeding in DIC, or you are desperate for a last-ditch effort to stop bleeding: give fresh frozen plasma. (these are all C recommendations, by the way). Do NOT give FFP for the sole purpose of a volume expander–consider albumin instead.
Here is a great overview from Utah Med Library.