Well not counting the DoW who by itself it's the greates mistake for the sheer unreadyness of Italy armed forces, basically try to fight everywhere without the resource. Concentrate it's assets in specific campaign help surely the armed forces in improving their performances, no wasting of men and weapon in Urss or in the battle of Britain or Greece, but concentrate in Lybia and Yugoslavia.
Second...someone must say to Benny to not improvise and plan ahead, the France and Greece campaign were hastily planned, basically he say the general to invade that countries immediatly and resolve the problem, plus with the sudden DoW Italy lost the bulk of her Merchant Marine with a little of planning a lot of ships can be saved and their cargo can reach Italy, a little thing but everything help.
Frankly with her situations the only sane thing in WWII for Italy was to declare neutrality,try to avoid conflict with every power except when a winner was clear, continue is modernization effort, grab everything she can from Yugoslavia and be ready to sell very well his aide against the soviets after the war.