Good readers use pictures, their knowledge of sounds and letters, letter blends and the shapes of words, experience of subject matter and the flow of language to help them make sense of the text that is laid before them.
Reading is very much a holistic experience for them and they look for meaning in the words they read.
They also self correct - if something doesn't make sense, they will try it again and go back and correct themselves.
Typically, poor readers don't look for what the text means. They look at it letter by letter, word by word.
They don't use all the clues in the surrounding print and by the time they get to the end of the sentence, all meaning is lost.
They haven't grasped the flow of language or looked for meaning in other areas of the text, such as pictures etc.
The reader then gets caught up in a vicious circle whereby because they are not good at it, they don't do it often enough which then makes it even harder for them to catch up.
Some of this information has been sourced from the book "Parents, Teachers, Partners" by Barry Dwyer.