Where to start. Here's everything I've learnt from six months of my first startup.
Any advice you're given, take with a pinch of salt. You learning on your feet is the only really valuable way to learn.
Give a shit. About everything. Your product, your reputation, your fellow founders, your customers. Give a shit some more: if you fail you should feel terrible. Boy will your friends mock you. Thats critical as this way you'll try harder not to fail.
Read The Four Steps to the Epiphany. Now. NOW.
Be cheap, lean and fast. And by that I mean really fast. Someone somewhere else is working on a product thats better than yours in every way, your only way to win is to launch before them. And by cheap I mean really cheap. Seriously, 90% of all startups are neither cheap nor lean.
Outsource stuff that isn't core: analytics, metrics, email, hosting, monitoring, feedback systems, literally everything you can.
Get your proposition awesome and simple. Like, if you can't define what you're doing and why thats valuable in under a paragraph try harder.
Simple is good. Simple revenue models, simple products, simple infrastructure, simple internal nonsense. Simple is more.
If you're raising money take money if you're offered it. Would you rather own 100% of nothing or 75% of something? Are you building a product or are you raising a fund? Its the former, take the money because the opportunity cost is too great to fuck about for six months touching VCs.
Revenue impresses everyone. As does a termsheet.
Know where you'll be in 3 days, 3 months, 1 year and 3 years. Make sure the 3 year goal is to be stomping on a publicly listed company.
Marketing is a black art, I don't think anyone is good at it without having a pre-existing tribe. Solution: start early, communicate with potential users, start the conversation. Look down, are you blogging? If you're not you've stumbled at the first hurdle. Don't bother planning too much for marketing: You'll do better on your feet, focus on product management now.
Product management is hard. Get users. Learn from them. Respect them. See #2.
If you're not a designer keep your UI and design simple.
Respect the UX else I'll stab you. Seriously. I don't care what you're doing, but there should be an emotional attachment to using your stuff. Even if you're a text editor: make the user feel like they're in the zone. AND DON'T CONFUSE UI WITH UX FOR THE LOVE OF GOD. Mac developers usually nail UX. Learn from that.
You'll be told you'll fail, or that people don't want your product, or that you should do something else, or that what you're doing isn't big or valuable enough (trust me, I hear those all the time) -- fuck them. Prove them wrong. You're an entrepreneur (god that word sucks) - if I told you to jump off a bridge would you? so why would you listen to me when I said stop? prove. me. wrong. See #2. Thats a force to be reckoned with.
I'll leave you with the the most powerful story (i'd love a source, i'm terrible at story telling) I've been told. ever. :
A few years ago a young girl decided she wanted to swim across the channel. so she did. however a few hours into the swim she got tired and felt like crap. it was raining and foggy. miserable. so she called it quits. it turns out she was about 20 minutes swim from the shore, and would have done it in record time. If only she hadn't quit.
My point is, when the going is toughest, and it looks like all the chips are down. they might not be. and imagine how sick you'd feel if you gave up so close to winning?
Oh and if when you chat to your co-founder you aren't blown away and left with a "whoa." you've probably chosen the wrong dude.