What's one thing you wish you'd known before signing your rental contract?

Looking back, is there anything you wish you'd understood before agreeing to your current lease?

It could be how the points system works, checking whether the rent was actually legal, understanding service costs, knowing what your landlord is responsible for, or simply being more aware of your rights as a tenant.

What advice would you give someone who's about to rent their first place in the Netherlands so they don't make the same mistakes?