Two ways to build a puzzle
Start from a finished answer and add clues around it, or start from clues and solve as you go. Both end the same way: test for one solution.
How it works
There are two ways to build a puzzle, and most setters use both.
Solution first. Draw a finished, legal answer. Then add clues that the answer satisfies, such as regions, numbers or givens. The answer is guaranteed to fit. The risk is that other answers fit too.
Clues first. Place a few clues, then solve as far as you can. Where you get stuck, add a clue that lets the logic continue. You control the path the solver takes, but you have to check that some answer still exists.
When to use each
Solution first is quick and suits puzzles where clues come from the answer: Queens regions, nonogram numbers, Slitherlink counts. You usually end up with too many answers and tighten the clues.
Clues first suits puzzles where you want a particular break-in or a particular trick in the middle. You set the first clues to force the opening, solve, and add clues only where the logic needs them.
Always finish with a test
Whichever way you build, the last step is the same: count the solutions. One is right. Two or more means add or reshape a clue. None means a clue contradicts the rules, so remove or change it.
Worth memorizing
Solution first: draw the answer, then add clues.
The answer always fits. Check that nothing else does.
Clues first: place clues and solve as you go.
You choose the path. Check that an answer exists.
Either way, count solutions at the end.
One is a puzzle. Two or none is a draft.
Practice
0 of 6 rightDoes this Queens puzzle have exactly one solution?
Does this Queens puzzle have exactly one solution?
Does this Queens puzzle have exactly one solution?
Does this Queens puzzle have exactly one solution?
You drew a legal answer, then drew regions around it. What is the risk?
You placed clues first and solved as you went. What must you still check?