When gaining facility in a language, we tend to want too much too soon, hoping to memorize more vocabulary than our brains can be expected to handle within a short time. In fact, many techniques in vocabulary mastery are geared towards being able to familiarize with words in bulk.
Granted, it is possible to learn more than one word a day. In fact, early in your language learning, regardless of whether you’re taking a course or are using a language software, you’re likely to pick up the basic elements of the vocabulary pretty quickly.
Unfortunately, this trend rarely lasts. As you work with a larger volume of words, you retain less of what you study, perhaps even finding it harder to comprehend more complex concepts. During these times, you can either keep working at it using the same techniques that worked for you early, give up or try to do things another way. I recommend the latter.
As you progress from basic vocabulary to gaining a wider range of competence, it might be more helpful to focus on mastering a single word per day. What exactly does this mean? Pick out a word that has relevance to the things you are involved with in your life (e.g. business, art) and try using it during the course of your day. In your practice time, try writing numerous sentences with it and reciting them. See what parts in your everyday life it is involved in and identify them as you involve yourself in your regular activities.
One word a day is hardly too much. Since you’re focused on it, you’re likely to be able to both retain it as well as integrate it into your ever-expanding vocabulary.