well you look at a few things at first and you will learn the more subtle aspects later
A.Speed for instance, the opposing pitcher today,Verlander, was hitting 100MPH consistently on his fast ball thats amazing for a pitcher the average is around 94 on a Fastball, I think.
B.movement, some pitches have natural movement on them like curve balls that obviously curve in an effort to fool hitters the bigger the movement the better the pitch.
and there are many more ways to tell when a pitcher is pitching well but those are at least how to tell each individual pitch for starters. and if there are no runs and no one on base most of the game then the pitcher is probably doing pretty well. so chances are with alot of movement and great placement its the pitcher doing well. if he is giving up alot of base hits but getting lucky and getting out of a lot of jams then its probably ineptness on the side of the runners.