When you start reading around here about making yeast starters, you will see a lot of different information. There seem to be about two hard truths that are common though...
1. When using liquid yeast, you should make a starter.
2. When using dry yeast, just rehydrate it and pitch without a starter.
There is also a general consensus that you need to prepare a yeast starter wort that is about 1.040 OG, which works out to about one cup of DME per quart of water. The actual volume of wort you prepare can vary from anywhere between one and two quarts to as much as 4 quarts for a big batch of big beer. I have had really good luck with one quart of water and one cup of DME as a starter that runs for no more than 48 hours before pitching. I like to give it at least 24 hours and up to 48, depending on my schedule.