First of all, you should consider the grounds on which you were rejected. If you believe that the rejection is incorrect, we recommend finding an advocate to help you to appeal. The Disability Advocacy Finder is a good resource for doing this. You can also submit a new application after three months have elapsed since the previous rejection, if you feel that you are in a position to make a better application. This may be faster than working through the appeals process.
You may also consider applying for aged care for under 65s. In order to get an aged care assessment, you must have a letter of exhaustion (a second rejection letter suffices) from the NDIA. It may be worthwhile getting an aged care assessment, even if you plan on appealing your rejection.