I have applied seven times for Singapore PR and got rejected every time. What can I do to make sure that I do not get rejected again?

If your application was not approved seven times, there has to be some reason for it. There could be an issue with your case that you may not be seeing. It is best to hire an immigration specialist to review your profile and documents. If there is a fault line in your case, the immigration specialist will inform and help you rectify it. ICA checks for a number of factors for PR, and lacking in even one of them may result in a rejection.