I don't think keeping a vocabulary or a notebook is a good idea while learning new words. When you write down the new words in a notebook you just remove these words out of your mind. You don't try to remember them. At the same time you are very pleased to have them in your notebook, not in your mind. It's much better to look the new words up in a dictionary and use them in different situations. You can also write them out on a piece of paper and have a look at them several times during the day. Never keep these papers, throw them away in the end and keep the words in your mind.