You should start by asking yourself the following questions: why are you considering a doctorate, what exactly does a doctoral programme involve and what skills will be required? As a PhD candidate, you must be able to work and write independently and have:
A doctoral programme primarily involves research. You must enjoy getting your teeth into a subject and exploring it in depth. And as you pursue your research further, it is important to be able to distinguish between primary and secondary issues and to make connections between the data you obtain and the insights you acquire.
The main criterion for admission to a doctoral programme is academic quality: you must be fully conversant with the theory and methodology of your discipline. There is also a legal educational requirement: you must have a Dutch Master's degree (or an old-style initial university degree) or a foreign equivalent.
Not all foreign qualifications, including Master's degrees, will gain you access to a doctoral programme in the Netherlands. The same applies to prior studies abroad which grant access to a doctoral programme. These are not by definition equivalent to a Dutch Master's and will not grant access to a doctoral programme in all cases.
As well as a good prior education, you must also have a good command of English, since this is the lingua franca of the academic world. Moreover, the relevant Graduate School or research institute may have its own specific requirements. These can be found in the PhD vacancy description.
To help you decide whether doctoral research is really for you, you can: