I was a co-founder at a SaaS health startup that ultimately failed because our team imploded. I learned a variety of very useful lessons from our failure.
#1 If you do not have strong domain expertise in your target market, your co-founder must. If none of your co-founders have strong domain expertise, you are in for a world of pain. It's possible to succeed without someone from the industry onboard (and we almost did) by figuring stuff out for yourself through talking with customers, but not having that person makes things 1000 times harder. Apart from having to spend a lot of time learning the domain, you also miss out on low hanging fruit initial customers / advisors who an industry cofounder would be able to acquire through their network.
#2 This is related to the first point above, but if you can, try to get angel funding from someone from the industry. Our angel was able to put us in touch with several industry players and regulators who were incredibly helpful.
#3 Before you start any venture, you need to sit down with your co-founders and explicitly agree on what the mission of the company is, what everyone's expectations and desires are, and what everyone's responsibilities will be. Take a decent amount of time to do this, put it in writing, and have everyone sign it. In my company we had three people with the title co-founder, all of whom had different ideas about what being a co-founder meant. One co-founder really wanted to be an advisor and never did any work, another co-founder really wanted to just be CTO and didn't really want to deal with non-technical matters, and I was left doing most of the day to day work. We also had 3 different opinions on risk tolerance and persistence. If you can map things out beforehand then you can hold people to your agreement when they aren't pulling their weight.
#4 Be flexible with your team. We had an initial product idea that didn't work out and we needed to pivot. Unfortunately the team that was a decent fit for the first space was not the right team for the second space. Don't be afraid to be honest about what the new requirements are and to let people go if you are still in the early stages and some people can no longer add value.
#5 If a vendor, advisor, or other entity says they will do something for free for you, it means they won't do it. We had 3 entities offer us free services because we were early stage and none of them actually did real work when push came to shove. Demand solid contracts from your vendors and demand to pay them.
#6 Hold off on incorporating until you have to. I spent an inordinate amount of time dealing with incorporation bullshit, tax bullshit, and compliance bullshit when we didn't even have a product and were still doing early stage work. Don't do this. Wait until you are at least ready to start development before you incorporate.
#7 Very few ideas are truly unique. A bunch of people probably failed at what you are about to try to do in the past. Do your research and figure out why they failed. Perhaps even try to reach out to them. I would gladly talk to anyone that asked me for advice or information on the state of the industry / product space.
#8 Get an accountant. There is SO MUCH TAX BULLSHIT and you don't want to be dealing with it yourself.
Ultimately we got unlucky in that our primary venture was in a space that was undergoing tremendous regulatory upheaval which made our product irrelevant, but given the nature of our team and circumstances, I'm not sure we would have had success even had the space not changed rapidly.