Puzzle can be tricky. Not being able to see something can turn a rudimentary challenge into a nightmare. Consider a well drawn diagram or props if it isnt a language based puzzle or riddle. I would also look to video games for examples. Click and point adventures are a treasure trove of the type of "solve puzzle to progress" puzzles you seem to be looking for. And one last piece of friendly advice: Leave two more clues than you think you'll need, and make sure at least one is obvious.

As far as sources: I've gotten quite a bit of use out of "The Game Master's Book of Traps, Puzzles and Dungeons." There might also be older edition books you can find pdfs for online.