Twenty minutes in your lunchbreak everyday can improve your skill considerably. Learning a language is not hard, and you shouldn't feel like you can't learn it. After all, you already know one - your native tongue. Children learn much faster than adults, often at rates as high as 10 words per day. They feel embarrassment at getting a word wrong, and hence become unwilling to try.
Children typically learn from everything - TV, radio, books, adults, games, play etc.
Be like that - vary the ways you learn the language. See the Online Hebrew Tutorial for some other resources. If you enjoy something, you will spend more time doing it. In a metaphoric sense, specific memory may be said to grow stronger and stronger as practice proceeds. The rate of forgetting is slower when the degree of learning is greater.