When critiquing the first page, note the use of dialogue. Is it natural? Stilted dialogue can break the illusion of the story. For example, 'Hello, how are you?' in a very robotic way is not good. Also, the mood is important. A dark and gloomy mood can be set with words like 'shadows clung to every corner'. The first page should also introduce the world of the story in a way that draws the reader in, whether it's a historical period or a fictional realm.
To critique the first page of a novel effectively, examine the character's presence. Are they relatable? If the character is a loner, show why in an interesting way. Also, think about the flow of the words. Does it read smoothly? Sentences that are too long or too short can disrupt the flow. Moreover, the first page should give a sense of the story's direction. It doesn't have to be clear - cut, but there should be some indication of where it's going.