Eagle eyes,
I'm new to the forum, but I'm an opera singer and have taught voice for 14 years. The problem with books, training videos, etc. is that they do not provide you with feedback on the sound you just made. So you are left to decide if you made the right sound or not. How would you know if you did it right? Add to that the fact that there's hardly any standard for terms (one person says this sound is falsetto, another says this sound is falsetto, etc.), so even if you were able to make a falsettic sound, would it be the one they were instructing you to make?
The best, most efficient way of improving one's singing voice is to take lessons from a good teacher. Teachers are more and more offering Skype lessons, and those can be good if you have no one decent locally. In-person is ideal, but if all else fails this is a good option to get the right instruction you need. Be sure to listen to how the teacher sounds and also how their students sound if at all possible so you can fairly judge if they are good. Lots of weird teaching going on these days with bad results.