You mean the criteria for producing a high quality rip? They can not easily be summarised in spec form since it varies from rip to rip, therefore the way to ensure how to get the best rip, is ensure you follow a correct ripping method. Follow gknot guides, and then use some very simple 'guidelines' below:
The major thing you need to do is drop AC3 unless needed..., its a very, very poor codec thats hardly compressed and still lossy at that! It should be reserved for at least a 2cd rip, never
a one cd rip (barring act of god circumstances). Hopefully AAC will take off and we'll get a surround sound codec to rival mp3
You should aim for 90mins = 1cd, don't go below 512x resolution, try and keep the bits/pixel as high as possible.
It's all about maintaining the balance between video and audio, video takes the focus of affection, 128 VBR mp3 is sufficient and will provide a quality 1cd rip.
Reserve AC3 only when a) the movie actually has a good AC3 track, full channel usage/soundtrack/sound effects b) you are doing a 2 or 3cd rip.
However, read this:
and the sticky above this.