The strategy, Tyrion's strategy, was for Dany to be loved as ruler above all else.
Landing on Dragonstone like Aegon, having Westerosi allies surround Cersei and proclaim Dany queen. Tyrion might also have suggested Dragonstone to keep the Dothraki out of Westeros as raping and pillaging would have built up resentment for generations.
The plan would have been fine if not for Euron bringing his ships to Cersei's aid and Randyll Tarly bringing support of the Reach lords. Tyrion miscalculated how able Cersei could gain allies, perhaps naively supposing that the Lords of Westeros would welcome Dany rather than fear and band against her.
Really Dany should have listened to Daario. She is a conquerer, she should have immediately have taken Kingslanding and installed herself as queen, everyone would have bent the knee once she was in place. Her hand seems to be forced now, she must take on Cersei directly, she must take Kingslanding, queen of the ashes be damned.