1. Build something that you're an expert on, and know how to build it. You can't do it all, but knowing how to do most of it goes a long ways. Hire out for the rest.
2. Be intimately aware of what the product should be from the users standpoint. What does it do that no one else's does?
3. Prepare yourself for supporting the business and support issues. You can't "back out" or dodge anything, and you've got to be ready to be in the hot seat alongside your uses. I've been told a "volunteer" type mentality is what this is called.
4. Be emotionally ready for an absolute roller coaster. One day you can be on HN, and that same day you'll lose your #2 account. It, by all means, is an absolute emotional washing machine. Try and distance yourself from the product if you can.
5. If your boot-strapping yourself then your limitation/runway can be time. Time does have a value aspect to it, and if you're an engineer you can grossly underestimate how long something will take to build which it's effectively money lost.
There's so much that goes into it, and every business is so different that it's hard to capture what to do. You really have to _just do it_ because getting started and out is the hardest part. Everything else seems to fall into place after, assuming you don't close it or abandon it.