Hold People Accountable to Defined Success Criteria, not your Opinions
New leaders often struggle in holding people, especially when they were recently peers, accountable to perform at a certain level. This is especially hard in organizations that don't have clearly defined success criteria for a role or specific leader.
As a new leader, it's important to clearly define what success looks like. This may be a set of goals (e.g., OKRs), or performance metrics such as revenue dollars booked each quarter or software features deployed each build. What's important is to have a clearly defined expectation for each of your employees, which they understand and have committed to meet. Then, if they don't meet expectations, you aren't the "bad guy" attacking them -- the expectations are the "bad guy", and you are working with them to determine if they are able to meet those expectations or not.