Depending on the university, you will either land your PhD position by applying to a doctoral program (common in the US), applying for an open position (common in the Netherlands), or applying for a new position if you are bringing your own funding (also an option in the Netherlands). It's technically possible to land a position in the Netherlands by cold emailing a professor (that was my path into TU Delft), but most cold emails will just get deleted.
If you want to get hired on a PhD position in the Netherlands through a cold email, remember first and foremost that your chances are low. It all depends on whether the targeted professor at the moment has a vacancy or not (or if you are bringing funding).
To grab a professor's attention when you write them, I have the following advice:
1. Do your homework
If your interest is in topic X and you write a professor in field Y, it shows that you haven't looked at their profile in detail. Most likely, your email will be deleted right away.
2. Make it specific
In my case, there was no official vacancy on the official job website, but the website of the research group mentioned they were starting a large project on the shear capacity of existing bridges. I knew for myself I wanted to do my PhD either on the topic of shear, punching, torsion in structural concrete elements or buckling of concrete columns. The topic called my attention, and my first email was an inquiry to see if they were still looking for researchers on this project.
3. Don't send the same email to all
Make your email personal. If you send the same email to all staff members of a research group, your message will not be personal enough to get the attention. If you contact someone in particular, make it clear why you want to work with him/her/them.
4. Explain why you would be a good candidate
It's not about your grades here - but why would you fit in a research group? Why would you be the right person? What calls your attention? If you are excited to do more lab work, mention it in the email. If you are a good team player, mention it. If you are simply passionate about the topic, and this topic really is what you want to dedicate your time to for the next years, let them know.
5. Call the attention
What makes you want to do your PhD there? In my case, I had heard about the professor who became my thesis promotor, and I was curious and eager to work with him. I've had emails of students explaining me they had started a program in a different university, but were wanting to transfer for a certain reason - those personal stories really get my attention. I may be more inclined to help someone who is willing to open up and let me see the real motivation of writing me.