For a novel to be great people have to want to read it. To discover the recipe for a great novel you have to discover what people want to read. We all have our own reasons for enjoying the books we read, but are they the same as everyone elses? Ah if only this were easy to discover, we'd all be bestsellers. Getting inside other people's heads is no simple task, but there are tools out there that will help you do it. Don't worry, you won't need a degree in psychology.
The first thing you need to do is to read new books in your genre. Pick up the bestsellers, get to know how those writers write, discover if they're bringing something new to the table. Join writers groups, either on line or in your neighborhood. Ask people what they looked for in a book of that genre, what makes them keep turning the pages and most importantly, buying more books by that author.
Keep up to date on the news in the writing industry. This can be done by following the blogs of agents and editors or by following them on Twitter, FaceBook, etc. Book mark sites that give you news of the industry. Such as http://www.publishersweekly.com/
The bottom line is, to write you must read!
Here's some great advice from an agent on ingredients for success: http://scbwiconference.blogspot.com/2009/08/sarah-davies-recipe-for-writing.html