Patiences, young grasshopper. When you fully understand how to construct a TCG deck, you will learn how to rate one as well.
But in all seriousness, to rate a deck, I've learned a few things from Trachy, but one rule of rating stands out above all else: Kept the original concept of the deck. If its a Trainer-block deck, well, don't take out the Gothitelle! :P
Then there's the actual construction of the deck, which is really complicated and involves a lot of thought, concept, and reality, as well as knowledge of how things turn in TCG.
TCG isn't all that different then making a team. It all has to work together to function, and it has to cover all fronts, while still maintaining that certain concept that keeps it unique. Explanations and info on the card and why its there will help in the over-all assessment of the deck.
Yet it all has to do with the understanding of the current format.