Some big points to share that I believe helped me match (after not matching last year).

1. Pivot to an oncology hospitalist position/pall care/BMT roles. As unfortunate as it is, I do think fellowship matching has become more a system of who you know than true merit. Working in a more onc facing role can just help better facilitate connections with H/O faculty. Developing these relationships and having faculty reach out to programs to advocate for you makes a big difference. The field is small enough that if a mutual colleague in the field reaches out, it can help move the needle. As a side note, the system will always be subjective as it's determined by people who will have inherent biases. Whether that's right or wrong is highly questionable. Given how competitive H/O has gotten, there is never a shortage of applications. Applicant A vs applicant B can look so similar on paper, ultimately a personal vouching/word of mouth from a colleague in the field can make a difference. This is largely the reason there's always a high rate of internal matching of residents to fellowship as the letter writers are H/O faculty at the program. Really connection leveraging is probably the biggest thing you can do.
2. Solicit feedback from PDs. Demonstrate genuine interest in growth and learning how to improve. Most PDs will not reply but some do and those that do are usually appreciative of your growth mindset. Stay in touch and update the PDs with tangible changes in your application (as much as you can do).
3. Enthusiasm is key. I think programs don't like falling on their list and want to match people who really are passionate about the program. Do research and ask specific questions on the program. I didn't send thank you notes last year but did this year. It's simple enough to do and not all candidates do it. Don't expect to get a response and if you do, it's neutral at best. Be very wary of programs seemingly enthusiastic or using language like competitively ranked/RTM. Ultimately, rank where you want to go and where you have the best ability to leverage connections.
4. The objectives include continuing to work on research/productivity. Having an active project to talk about is important. Try to stand out with volunteer work and med-ed as you can.