Ditto to #6's suggestion of reading a summary of the chapters beforehand so that you can more easily focus upon the beauty and style of the prose. It also is helpful to understand Mary Shelley's motives for writing the novel. Do not hesitate to avail yourself of Enotes's summaries, character analyses, etc.
Frankenstein is truly an interesting and well-written classic. It is one of those "frigates" of which Emily Dicksinso writes of books that carry you to new lands!
I really love Frankenstein, however, I find Walton's letters at the start really dry. Shelley praises the "landscapes" of what the captain sees, but we also get the sense of his obsessive behavior, which is probably the most important element of the letters...so we can draw a parallel with the way Victor acts in creating the creature. Later we see Robert Walton's willingness to sacrifice his crew for his dream, the way Victor was willing to sacrifice the safety of his family and society by releasing his creature on the world, failing to assume his responsibility. If you can scan through the letters, I think the story itself becomes much more interesting.
If you review the story's themes before you read, this information might be beneficial in helping you to understand what drives the story. I would also make sure to put yourself in the creature's place to better understand his motivations. It makes the story much more interesting when we realize that we're not quite sure who the real monster in the story is.
Great novel, and I think you find that as you begin reading you will get used to the style and the language that is used. What is important to realise first up is that a framing narrative is employed which starts off with the story of Robert Walton, who is trying to find passage to the North Pole by ship. We start off with his story, and the narrative only shifts to the tale of Victor Frankenstein when Walton picks him up on an iceberg.
It often helps to read summaries of a chapter before reading the actual chapter. I know that this opinion is considered heresy in some circles, but it often helps to know what is going on before you try to read. If you are familiar with the basic plot of a chapter before you start reading, you are actually more likely to notice more valuable details as you read.
It may help to get an unabridged audio version of the text for i-pod. I had a version on cassette tape which was useful with the creature's parts. Also, I fiind reading such a challenging text in short bursts: 20-40 mins maximum, then writing down a line or two about what you have learnt can help with the study of such a text.
I found my first reading of Frankenstein a tough read, especially the first half of the novel. It will get better and more exciting, so hang in there. It's a classic, and I'm sure you'll feel the reward upon completion.
It will be interesting to see what specific questions you have as you go. Basically, you need to understand that the novel begins with these letters from Robert Walton (English explorer in the Arctic) to his sister. These letters sort of lay the foundation for what is going to happen next. We are seeing the end of the story here at the beginning of the book. After the letters, we will go back in time and find out what led to this ending.