How difficult is it to get into JBIMS, Mumbai considering the fact that the candidate is not a resident of Mumbai?

As long as you are a Maharashtra resident, getting admission to JBIMS is not that difficult. Out of 120 seats, 102 seats are allotted to Maharashtrian candidates and the additional caste card will further increase your chances. Other than Maharashtra you will have to target 99.99. To ensure a good CET score 

• Prepare well for CET and strengthen your basics
• Attempt a lot of mocks
• Pay more attention to logical reasonings 
• In the quant section focus on m DI and DS the most 
• Practice visual reasoning thoroughly 
• Improve your speed and efficiency 

If by the difficulty you mean the probability of getting into JBIMS then here it is. Out of 100k candidates, only 120 are selected. For some, this may be a discouraging factor but if you look on the bright side, being along the 120 will guarantee a bright future.