Don't give up.
Firstly, make sure you have examined every item in every location, including scenery, as this will sometimes expose a new item, give a subtle clue or just provide more detail.
Secondly, make sure you draw a map. It's amazing the number of times a player misses a location, simply because they've missed or forgotten an exit because they didn't draw a map.
Thirdly, write yourself some notes, things like:
- What objects have I found that I haven't used.
- What obstacles are preventing progress.
- What puzzles are yet to be solved.
By taking a more disciplined approach, you will quite often hit on a solution to whatever it is that has you stumped.
Fourthly, leave if for a day or two and come back to it with a fresh mind.
Finally, if you are still stuck, type HINT (if the game has in-game hints), ask a question in the Comments on the game page or look up the solution on the Classic Adventures Solution Archive (CASA) at https://solutionarchive.com/.