Comparing Wordsworth and Coleridge is a huge task, and I suggest you start a Discussion Group question with this to get as much information and as many ideas as possible.
That said, I'll give you some basics.
Wordsworth is famous for changing the diction thought acceptable in poetry, or at least strengthening the movement toward a "common" or simplified poetic diction. He took some of the formal language out of poetry and replaced it with simple, concrete words. "Common" may be too strong of a word when you compare Wordsworth with, say, contemporary poetry.
Wordsworth's poetry also emphasizes nature in a personal, lyrical way. Personal reactions to nature and insights gained from nature are paramount.
Coleridge, in contrast, emphasized the imagination. His poetry dwells in the land of fantasy. Whereas nature may receive the most emphasis in Wordsworth's poetry, the imagination is central to Coleridge's. His speech, in contrast to Wordswoth's, is exotic and imaginative. His language is the language of fantasy.
Those are some basics to get you started, but there is much, much more to this comparison.