There is no simple answer to this. It depends on the adventure and the individual. For me, I like to think of the time, the place, the puzzles and the objective.
By "the time", I mean when does the adventure take place? Past, present or future. Most adventures take place in the past. This gives them more character. The present tends to be a bit boring. The future tends to mean science fiction.
By "the place", I mean where does it take place? Is it on Earth or another planet or a fictitious world? If it's on Earth, what country and what city?
Once you have decided on the time and the place, start to think about what the scenery would look like during that time at that place. Is it indoors or outdoors or a mixture of both? What sort of buildings would you expect to find? How would the buildings be located with respect to one another? What sort of rooms would be in the buildings? What sort of locations would you expect to find if it's outdoors? What sort of objects would you expect to find in all those locations in that time period? Write lots of lists. Do Google searches on the time and place and before long, you'll have so many ideas that you won't know what to do with them all.
By "the puzzles", I mean what puzzles will you need to solve in order to meet the objective? It helps to decide on the time and the place before you start thinking about the puzzles. All the objects you thought of will start to give you ideas. Mix it up. Some objects should be in plain sight. Some should be hidden. Some objects should be found before you know what they're used for. Some should be found after you know that you need them.
The best puzzles are when you use common, ordinary, everyday objects in unusual ways.
Take lots of notes and be prepared to discard any ideas that don't fit the final game. It's okay to have a few red herrings (objects that serve no purpose), but try not to have too many.
And finally, to answer your question, yes, definitely draw a map and locate all the objects on the map before you enter any code. In fact, you should be able to write a complete walkthrough on paper before you write any code. It is much easier to see what works and what doesn't on paper than to spend lots of time coding only to find that you've got to change it because it doesn't work. Design, design, design, then code.