What does Philip Larkin try to convey in his poem "A study of Reading Habits"?
I just have a few things to add to the very comprehensive answer provided above. I would point out that in a number of Larkin's poems, there is a definite and deliberate discrepancy between the title and the ending of the poem. Larkin seems to delight in shocking his readers through the use of formal English in titles, such as his famous "This be the verse" and then the use of trivial and colloquial English therein. We can see this in this poem with the rather formal and pompous title of "A Study of Reading Habits" and the colloquial language that he uses to end the poem, where he argues that "Books are a load of crap." However, we need to be aware that Larkin is far more subtle than his poetry at first glance would suggest. Just as he is not really arguing that we should "get out" of life "while we can" and not have any children (his argument in "This Be the Verse"), he is not really arguing that "Books are a load of crap" in this poem.
Rather, what he is saying is that it is how we use books and literature can be unhealthy and dangerous depending on what we do with them. Clearly the examples that the speaker gives are rather unhealthy ones. The fantasy worlds in literature allow the less-than-physically impressive speaker to maintain some level of self-esteem through believing that he is able to show physical supremacy against "dirty dogs twice my size." Likewise, he is able to fulfill and gratify his sexual fantasies and cravings through literature, suggesting a rather disturbing and grotesque series of fantasies and sexual violence:
The women I clubbed with sex!
I broke them up like meringues.
The last stanza suggests that the speaker does not read because these fantasies have become "too familiar," which leads to the conclusion of the poem, which is vintage Larkin in its cynical and sarcastic viewpoint. For an academic such as Larkin, he is not seriously arguing that books are nothing more than "crap." He is pointing towards the excesses of imagination and fantasy to which they can be used. This is the "study of reading habits" that is explored through the poem.
Phillip Larkin's "A Study of Reading Habits" is a dramatic monologue in the tradition of Robert Browning ("My Last Duchess," "Fra Lippo Lippi") and T.S. Eliot ("The Love Song of J. Alfred Prufrock," "Gerontion"). To understand what Larkin is trying to convey, we must distinguish between what Larkin's speaker says and what Larkin himself is trying to convey.
In the first stanza the speaker's tone is bitter and sardonic ("getting my nose in a book / Cured most things short of school") as he discusses his childhood. He suggests that reading consoled him during this period. Next Larkin offers an implicit contrast between the speaker's actual physical apperance ("with inch-thick specs") and the fantastic image of himself as a vampiric deviant ("Me and my coat and fangs") he has crafted, drawing upon his reading. The final stanza begins with an announcement from the speaker that he no longer possess the "Reading Habits" of the title ("Don't read much now"). He then proceeds with a short catalogue of narrative cliches (the dude / Who lets the girl down before / The hero arrives, the chap / Who's yellow and keeps the store / Seem far too familiar"), which he seems to offer as evidence toward his final conclusion that "Books are a load of crap."
Larkin seems here to suggest, pace many contemporary apologists for reading, that reading for reading's sake does not benefit individuals or societies. When the poem's depraved speaker read books, he did so alternately trying to make himself feel better about his obsure situation in life and in order to indulge his violent sexual fantasies. All of this becomes complicated, of coures, in light of our posthumous knowledge of Larkin's very developed interest in sadomasochistic pornography.