First, understand the fundamental reason which led to the loan rejection. Then:
Ask questions - engage your lender in an open conversation to understand why your initial application was not approved. Your lender might give you more tips and helpful advice, so listen to it carefully.
Create a checklist - based on the information you get from your lender, create a list of your requirements. Note down what you lacked during the first application and think to turn lender's no to a yes.
Work on your credit score - try to improve your credit score if that's the reason as to why your loan was not accepted.
Pay your debts on time - take every possible step to pay back your outstanding loans faster. This might open up new possibilitites for you to finance your needs without even borrowing money.