- Related, getting authorship (first or otherwise) for an academic publication as an undergraduate is a promising signal of future research success.
- Also related, having great references from undergrad professors who are involved in research.
- Connect with faculty in the PhD program you're interested in.
Context: Got bad grades in undergrad courses related to my particular specialty (digital audio signal processing), but also did all of these, and was admitted to a top PhD program in my field.
Also, a lot of people in my program had success with this one:
- Applying for a masters in a related field or at a department that also has a PhD program that you're interested in, and having success there.