I'd somewhat change #1 to "starting and starting often." I see far, far too many art students fall into the trap of wasting hours finishing work when they'd be better off starting more pieces.
1. Start often and finish often; do not be afraid to abandon something that is not working. Learning what is not working will come from starting and finishing more often over time, along with reflecting on the work you have done. This is where the benefits of #3 come into play. A good community will not only praise your work, they will tell when something isn't working or doesn't work.
The wasted hours are the hours that they are not working on the thing. One hundred hours is only a bit more than four days...and if you use both hands, barely more than two.