You should look at solutions only to compare with your own.
If you can't do a problem, looking at the solutions is a bad idea.
Instead, you should re-read parts of the book that seem relevant to that problem, and then try again to solve the problem on your own. Sometimes it takes a lot of thinking and several tries (with hours or days in between the tries).
The next best way to learn is to get hints from me or someone else.
The worst way is to just look at the solutions!