We all cannot be like the Shaolin monks and devote hours upon hours a day to martial training. It is hard to find time to train when you have a fulltime job and a family (or whatever life demands are placed upon you). What we can do is apply intelligence to our practice so we can maximize the time that we do spend.
Persistence - persistence is a key component of practice. You have to set aside time that you can practice regularly in order to get the full benefits. It does not have to be huge chunks of your day, the key is consistency.
Precision - Set a few minutes aside to try and come up with a precise goal for your practice session. it could be something you are trying to improve, like getting better at using a particular technique. Having a precise goal in mind and focusing on achieving that goal during practice are a great way at improving as a martial artist.
Progress - You have to continuously seek to modify your practice so that you are progressing. Maximize the intensity of your workouts so that you can gain the most benefit. It is also a good idea to record your workouts so you can note your progress, this will give you a better gauge as to how you are progressing and allow you to tailor your practice if need be.
Patience - realize that true mastery may take years, enjoy the journey and remember that skill takes time to develop. Kung-Fu is mastery through time and effort, you need time to incubate your effort and see it come to fruition.
The secret to Kung-Fu and all other martial arts is there is none. The difference between a great martial artist and the beginner is not "innate natural ability" or being gifted, it is countless hours of practice. I'll end this with another quote from The Art of Peace.
"Progress comes to those who train and train; Reliance on secret techniques will get you nowhere." - Morihei Ueshiba