Business side, everything that can be useful to find partners, customers, raise funds.
Maybe you can suggest some books or read list.
[1]: https://news.ycombinator.com/item?id=5591319#up_5591574
0. The Four Steps to the Epiphany - it's not strictly about "marketing" in and of itself, but it certainly touches on elements of marketing, and should be required reading for any startup founder, IMO.
1. Crossing the Chasm by Geoffrey Moore (more marketing strategy / product strategy than marketing tactics, but a valuable read)
2. Lookup the current textbook for "Marketing 101" (or it's equivalent) at a nearby college. Go buy the book and read it, even if you don't take the class. If you have time and money, take the class.
3. The Ultimate Sales Machine by Chet Holmes. I'm deep into studying Chet's approach now, and his book has some great stuff on it. If you can, get hold of his videos from the program he did with Anthony Robbins titled "Ultimate Business Mastery System." You can safely skip the Tony Robbins part, but Chet delivers some good stuff.
4. In Search of Stupidity by Merrill Rick Chapman.
5. Positioning: The Battle for Your Mind by Al Ries, Jack Trout and Philip Kotler
6. The 22 Immutable Laws of Marketing: Violate Them at Your Own Risk! by Al Ries and Jack Trout
7. Re-Positioning: Marketing in an Era of Competition, Change and Crisis by Jack Trout and Steve Rivkin
8. The 22 Immutable Laws of Branding by Al Ries and Laura Ries
9. Differentiate or Die: Survival in Our Era of Killer Competition by Jack Trout and Steve Rivkin
10. Successful Business Research: Straight to the Numbers You Need - Fast! by Rhonda Abrams. This is good for learning about how to find the numbers you'll want to use to put together a first cut of a marketing plan. Think your "target market" is "screw, nut and bolt manufacturers in the southeast with more than 500 employees"? Then you need to know how many of those even exist, before you know if the market is even theoretically worth pursuing. Think your market is "adolescent girls in Massachusetts?" Then you might want population demographics and birth rates, etc. This is a good basic, (and cheap) book with some good pointers on how to get started on that kind of market research.
11. Marketing High Technology by William H. Davidow
12. How to Drive Your Competition Crazy: Creating Disruption for Fun and Profit by Guy Kawasaki
13. I'm a big Seth Godin fan, I'd say read anything and everything by him. The Purple Cow stands out in my memory as a particularly good one. Permission Marketing is good as well.
14. The Cluetrain Manifesto
Also, I don't have any specific titles handy (I'm out of town consulting right now, unfortunately, so I can't even walk into the other room and check), but just go to a good used book store near you (if you have one) and find a couple of cheap used textbooks on "marketing research" and "marketing strategy". The exact title won't matter, you just want something you can read through and get the high level stuff. You're not trying to become an MBA, just to learn the language and the broad brush stroke overview of what goes on.
Some more suggestions in another old thread: