Something which I often recommend to my juniors in the art is the act of visualization. I find that many may think of this as supplementary or perhaps unimportant, but I could not disagree more. When I have been busy, or otherwise unable to train, I found that visualization was not only vital to maintaining my mindset, but also in sharpening my abilities. The ability to picture your techniques, see yourself perform them against an opponent, and then compensate for your mistakes, repeat the experience until you 'get' the correction you want, is vital to the dedicated artist.
Some of this was inspired, actually, from a few manage that I used to read. I know this is a unique and perhaps silly source from which to draw inspiration, but perhaps that is the point of inspiration.
There are several levels to training that we undergo, and hopefully we continue to grow in that respect. But we must also focus on the mental training that is available to us as experienced martial artists.
I must also say that visualization often coincides with breath training - I find myself unable to separate the correct breathing in visualization without doing so in real life. Perhaps this is a weakness in myself, perhaps this is a benefit of visualization. With the right breathing, power is magnified (just as in the manga - albeit to ludicrous levels). But in reading old texts and sayings from Okinawa and China, their belief in the breath was very strong, so perhaps this isn't an incorrect focus for study.
I have also found that visualization has another aspect of training can help to clear the mind (much like meditation) and hence improve reactions and reflexes. I think that watching videos is of similar benefit when you are trying to emulate a technique - seeing someone you find worth emulating perform the most subtle aspects of the technique not only give you insight into your own technique, but serve as motivation for future physical training.
As always, the way is in training.