Due Dilligence is an important stage in the investment decision process. It is realistically the last chance to spot that a potential investment has major problems and that as investors we should not proceed. Alternatively the due dilligence might identify serious weaknesses in the business, and lead to conditions on the investment to deal with these.

Below in the links, practical guidelines and a template to carry out your due diligence as an early stage investor.
Due Diligence Guidelines
Due Diligence Template
Due Diligence Checklist