How to feed heifer best?

[Northline Limousin]

I have a May '15 heifer that at the moment weighs approx. 650#. She just gets hay at the moment, nothing special, but I would like to start putting some feed to her soon to feed her up for my August-November Shows this year. I have heard 1-3% of their body weight is what you should feed? Of what? Should we mix fillers and high energy or just feed the cattle mix we get for the cows at the local mill (mix of molasses, rolled grain, a small amount of cracked corn, and rolled oats I believe)
Thank you everyone!
(Ps. Sorry the picture is upside down, I'm not sure how to fix it.)