You mentioned .. "push off the rubber.."
Well, not exactly. What plaz is suggesting is to keep your stride toe pointed towards the first baseline while striding down the mound with your stride foot, thus staying somewhat closed with your hips and other disciplines.
Pushing off the rubber:
It is my person view that, pushing off the rubber right now might force you to rush things a bit. Pushing off the rubber requires a lot of strength in the legs, core, shoulders and pitching arm, not to mention the ability to maintain your sense of balance while going down the mound and progressing with your entire pitching cycle. Trying to figure out the how-n-what for, during the time, might be complicated if you force yourself down the mound too quickly. Take a look at this ending posture of this pitcher, and let me suggest something to drive my comments home:
Now go to the mound and plant yourself down where your stride foot would stop, take this pose and HOLD IT. Then ask yourself ... "what muscle group is really feeling it right about now?" The longer you hold this ending posture, the more muscles will chime in and say ... "Hey guys.. this smarts.."
All in all, these muscles collectively are trying to tell you what should be worked on to strengthen what. Now, of course your pitching arm and your shoulder platform (muscles) aren't going to feel as much strain as the rest of your body - but then that's an entirely different composition not covered here, as of yet..
Now there are a ton of other things that go into what you're trying to do. My suggestion and plaz are just scratching the surface here.
I would like to point out that if you're going to start this learning process, start off right by developing a solid meal plan and nutrition schedule for yourself. In addition, don't forget a good sleep management program that allows you to get enough sleep so other things fall into place. Without good sleep habits, your eating routines will not be supported, neither will your attention span be supported, and a host of other things won't fall into place just when you need them - general injury recovery, endurance and tolerances, etc.