Since Robert Frost's style varies greatly between his poems, this might be easier if you choose specific poems to compare.

Emily Dickinson generally writes short poems. Some common themes she writes about include death, loneliness, love, etc.

Frost does often write about death- especially the poem "Out-out" and the poem "Home Burial". One poem of Robert Frost's that is similar to both Emily Dickinson's style and themes is "Fire and Ice"

Some say the world will end in fire,
Some say in ice.
From what I've tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To say that for destruction ice
Is also great
And would suffice.

This poem is similar to Dickinson's style because it is short, it rhymes, and it has a sing-song quality, much like many of Dickinson's poems. Its theme centers on the end of the world, centering on the way the world may face its destruction. Dickinson, however, usually uses more hyphens and more consistent line length. If you need to write a paper about these two poets, I'd definitely suggest choosing two poems to compare and contrast rather than trying to compare and contrast their styles in general.