An extremely important factor in making your beer is the amount of cells you add to your beer to ensure proper fermentation. In addition to aeration of your wort, your starter needs to be aerated as well. Once again, How To Brew has a fantastic explanation of the procedure on how to do this.
I usually start with 1 cup Malt Extract (any kind close to the color of your beer), along with 1 cup corn sugar. I add this to roughly 3/4 of a gallon for my starter. You can add hops to the starter, but it’s not necessary, and don’t add too much, hops will inhibit growth. Our cells need all the help they can get from their starting phase.
Depending on the health of the yeast you’re using, I usually build a starter until it looks something like this:
That dark matter on top of the foam is called krausen, indicative of a healthy culture. At this point, you should also see the liquid inside the vessel swirling around like crazy. This is yeast fermenting and generating CO2 gas from the fermentation. This start is ready to pitch into our beer!
Your pitch rate is extremely important for making great beer, and this article does a fantastic job on how to calculate this.