Quality is delighting customers
Experience based approach ... go for Exploratory testing .. Learn the application and then try to prepare test cases ... however, it is not recommended to prepare test cases in Exploratory testing .. but it may be an alternative ...
1) Is application is already developed then based on the application
2) any design docs are available then based on that
3) Nothing is there then based on your previous experience and knowledge of that type applications
1.Try to explore the simulated applications,so that perform exploratory testing.This type of testing is also encouraged with the support of Domain Experts.
Let suppose,if we have to working for Travel site (Flight) Then explore popular sites for Flights booking try to understand and assume the common requirements as an end user.
2.Its an alternative only ,If we dont have Enough time to perform testing, like prepone the deadlines case and If we dont have requirements info from client we wll perform exploratory testing.