A software startup is an emerging company focused on creating and developing an innovative software-intensive product or service as a basis for creating business value. Business incubators usually offer mentoring programs to help startups deal with the business side of new ventures, but they lack mentoring support on product engineering and construction. Based on the outcomes of two focus groups with mentors, software engineering practitioners, and software entrepreneurs, this paper proposes a mentoring process on software engineering aimed at software startups and a validated set of supporting guides for the software engineering practices and techniques most used in software ventures.