Firstly you need to define your goals. Do you want to: retire richer? Retire earlier? Supplement your income? Supplement your superannuation? Diversify your investments to spread risk? Give up your day job?
Buying the right type of property in the right location will help you to achieve your goal. It is important to establish what your goal(s) is at the outset because it will determine which strategy—renovate, develop or buy and hold, you apply.