The Moral-Philosophical approach to literature is an examination of a text's context in regards to the "philosophical thought of the time period or group." When examining Mary Shelley's Romantic novel Frankenstein, one would need to look at both the philosophies of the time period (the early 1800s) and the literary genre (Romanticism).
That being said, one would need to begin with a study of the time period. Research needs to begin with the political beliefs, religious ideology, scientific ideals, and morals taught during the 1800s. After examining the time period, one would need to examine the ideology of the Romantics themselves.
As a suggestion, when beginning to research the information required, one needs to begin with the ideology of the time period. By doing this, one can come to understand how the literary period was influenced, or contrasted with, other ideas of the time. After, the novel itself needs to be examined.
Therefore, the essay, in order to develop understanding (and proof of understanding) needs to open describing the time period first. The the essay needs to move in to the characteristics of the period. Lastly, the novel itself needs to be defined regarding how it "fits" into both the time period and the genre (or how it does not fit).
Research quarries have been referenced below in order to help.