Instead of going through investing in startups from a philisophical standpoint famed investor and excellent blogger Sam Altman has shared his viewpoints from the investor side as opposed to all the content that focuses on the startup side trying to raise capital.
There are so many great points on Altmans blog and in this post particularly with the biggest piece of advice IMO is not only tell the startup how you can help but show a genuine interest and ability to help. Often times a smart founder will take an offer that isn't as financially appealing on paper to get the help of an investor who can truly make a much bigger impact than one who just writes a check.
When we launched and were growing Protos Eyewear we had emails daily from all sorts of investors and partners but ultimately the most important end game contact came from Luxxottica the owner of Sunglass Hut, Ray Ban, Oakley, and just about every other major eyewear brand.
Read for yourself at: https://blog.samaltman.com/how-to-invest-in-startups