To all getting frustrated about perceived lack of progress: "The secret teaching is -- relax."
Tenzin Wangyal Rinpoche (TWR) in "The Tibetan Yogas of Dream and Sleep" (TYoDaS) offers this advice in the chapter of obstacles that arise in gaining lucidity in dream, in the section called "too much seriousness."

In summary, he sort of pokes fun at people, saying that after all, the practice is to see life and the practice itself as a dream, and here you are, being all serious about it, seeing the practice not as a dream but getting all serious and thinking it's a heavy obligation to bear.

He also recounts how people who have lucid dreams come to a dream yoga workshop and work really hard on the exercises for a month, and all their lucids stop. "When they see me, I tell them they've gotten too serious about everything. The secret teaching is -- relax."

In pursuits where the majority or all of the action takes place entirely in the mind, like dreaming, maintaining the proper mindset is just as important, if not more important, than the particular practices that one does to promote lucid dreaming.

I've seen this time and time again in my own practice, and you can see evidence of this in every LD forum/site anywhere: people work hard, have minimal or no results, give up, then BOOM they get a huge wave of lucid dreams all of a sudden. I call this the "I give up!" technique. It is a direct result of the relaxation that occurs, the relief of the pressure the practitioners have been placing on themselves in the practice, when they stop trying too hard (or at all).

Results do not come linearly or in even steps. They build up (and atrophy) slowly, gradually, over time. Know that if you are practicing a solid approach, like in ETWOLD or other well-recognized books (or from this book mentioned here, TYoDaS), and you practice the foundations (dream recall, awareness, reflection, intention, memory, lucidity itself) diligently, every day, without fail, you will improve in time. It may not be on the schedule you had wanted, but improvement WILL come. Just don't get in your own way with frustration, anxiety, stress -- these are mental blocks that will prevent dreaming and lucid dreaming from happening.

I see so many people setting themselves up for poor progress by treating non-lucid dreams as failures. If you start to associate negative emotions with dreaming, you can expect that your dream practice will not work out as you had hoped. Instead, I recommend developing a "dream practice," where you are additionally working towards more lucidity in dreams. Celebrate, love, enjoy, be very interested in ALL your dreams. Be thankful for your dreams. Gratitude has a powerful positive effect on the mind. If you develop a happy, light-hearted, joyous attitude toward your non-lucid dreams, if you can convince yourself ("fake it til you make it" if need be) that recalling and journaling your non-lucid dreams is the best part of your day that you look forward to with eager anticipation, then your mind eventually WILL respond with more recall, more vivid dreams, more presence, and in time, more lucidity.

This will happen especially if you adopt a practice where you are attentive, mindful, reflective, and work on remembering your experiences, throughout the waking day. The best progress will be found where you build a lucid life, as opposed to living mindlessly and on auto-pilot throughout the day, and then hope for bright, vivid, lucid dreams will somehow magically appear at night.

Tenzin Wangyal Rinpoche writes: "[if you feel the practice is becoming a burden], your practice is not going to work."

"The whole approach is to relax, take a deep breath, open, allow, trust. Allow the result of the practice to come to you. [Of course, this doesn't mean you do nothing. Do the practices, with intent], but also with an openness, ease, a relaxed attitude. If you become frustrated, you're trying too hard. Allow the result to come to you rather than working hard to make the result happen. Just let the practice be part of your life."