Great advice! If you think about a mathematical problem on your own first, you may come up with new ideas. Next, look at the literature to find the old ideas people have already tried. If you're lucky, you will see how to combine your new ideas with their old ideas to solve it.
How to use the research literature. When approaching a difficult mathematical problem, first think deeply upon it on your own, using all the ideas you can muster, before consulting the work of others. Push your own ideas as hard as you can first, and read only afterward.