As you are working toward unlocking that platinum trophy, it helps to get rid of the trophies you have already unlocked when you are reading the trophy guide. If you are logged in, you will be able to mark a trophy as unlocked so that it no longer appears in the guide. Here is how to use the trophy guide tool.
For each trophy in a trophy list, there is an icon to the right that shows the type of trophy that it is. If you click this icon, it will mark the trophy as unlocked and will automatically hide it on the page. The trophy will remain hidden, even if you refresh the page.
If you want to view the full guide, including the trophies that you have already unlocked, scroll up to the top of the page and you will see an option to “toggle unlocked” trophies. This will show all of the trophies that you have unlocked. You can click this again to re-hide them.
If you have accidentally marked a trophy as unlocked when you have not unlocked it, toggle the unlocked trophies and click the trophy icon again. This will remove the record that says you have unlocked this trophy and it will appear on the main trophy guide again.
Once you are familiar with using the guides, why not consider submitting a guide? If you find a trophy list without a guide, you can submit one from the same page as the trophy guide tool. At the top of the page you will see a submit guide button.