A good question has one job: to show what a student can do with what they know. Questions that only ask for a remembered fact are easy to write and easy to mark, and they tell you the least.
Change the situation, keep the idea
Take a worked example from class and change the numbers, the context or the unknown. A student who understood the method can follow it into new ground; one who memorised the example cannot.
Write the marking scheme first
If you cannot write down what a full-mark answer looks like, the question is not ready. Writing the scheme first also catches the case where the model answer and the worked solution disagree, which fails the students who got it right.
If two good answers could earn different marks, the question is the problem, not the students.
Ask for working when working matters
For calculation questions, award marks for method as well as the final value, so a correct answer with no working does not earn the same as one that shows how it was reached.