Beyond that, it's hard to say without more information. Have you looked at Startup School and their library[1] of information? If not, I suggest doing that, as it's a veritable gold mine of good information.

If what you're working on is intended to be a scalable startup (as opposed to, say, a laundromat, or a one-man consulting company, etc.) then I highly recommend reading either The Four Steps to the Epiphany[2] and/or The Startup Owner's Manual[3]. The latter is nominally the 2nd Edition of the former, but I find that there's enough difference in the content to justify reading both. If you're more enterprise focused, the former is more centered on that world. If you're doing something consumer focused, the latter title is more oriented towards that (but not to exclusion).

[1]: https://www.startupschool.org/library

[2]: https://www.amazon.com/Four-Steps-Epiphany-Steve-Blank/dp/09...

[3]: https://www.amazon.com/Startup-Owners-Manual-Step-Step/dp/09...