The main thing that Shelley does to make his poems more sensuous is use personification. This is where you take an inanimate object-like a rainbow or the moon-and give it human-like traits. That way, the object seems to come alive, to breathe, and to be able to possess human emotions and passions. In "Cloud", Shelley describes the moon as an "orbed maiden with with fire laden," which makes it seem like she is a beautiful young lady, clothed in a dress of white fire. This image is very sensuous; imagine a woman dressed in fire, and how beautiful, passionate and striking that would be. And, that is how he describes the moon. Then, he describes how the cloud (the speaker of the poem) binds the mood "with a girdle of pearl." This is interesting because it is describing the moon getting close enough to metaphorically be under her clothes, right next to her skin, like a girdle. That explanation is obviously sensuous, and describes the cloud, or the speaker of the poem, being very close with the moon.
He describes the rainbow as a "million-coloured bow" that is "sphere-fire" above the "moist Earth." Giving the rainbow a million colors instead of a few, makes it more intense and passionate. Calling it "sphere-fire" makes the soft light of a rainbow seem more like fire, and that takes its intensity up a notch; having it be over the "moist Earth" seems to indicate that the rainbow is a powerful being, with the ability to impact the earth.
I hope that these thoughts help; good luck!