What are the best practices to improve the efficiency of developers and leaders?

Staffing Management Plan , A component of PMBOK's Human Resource Management Plan comes to your rescue here
It covers things such as :-
Training
Rewards and Recognition
Compliance to standards
Safety

Do these staff members have adequate training to improve their efficiency?

Have they been recognized for their good work? Has that motivated them to improve their performance?

Have they been given a safe working environment?

Have they been given mentoring? have they been paired with an experienced programmer and undergone peer programming experience and exposure . Do they know what they need to improve on? Has the team leader undergone one -on-ones with them to make sure there are no inhibitors to their progress?

Have they been given soft skills training ? Influence, Emotional Intelligence, conflict resolution, negotiation, group facilitation?

Do you perform team building activities? Are you investing in their overall growth?

In addition to the motivation methods that have been stated by Deepesh, I would like to stress on Training that enhances developers/leaders skills and competences.

Empower growth and improvement:

Partnership - improved communication, expectations, and understanding between the BA and developers. Find the right balance of detail. Ability to convey the big picture vision and ensure they see it as intended. As the relationship grows, the connection increases.

Reuse - Look for ways to reuse existing functionality, avoiding redundant tasks and efforts. Build up you development library and classes for including in other efforts.

Documentation - Ensure all efforts are well documented with a Technical Design Document. The original developer won't be there forever. At some point, the solution will be enhanced or maintained by another individual.

Best Practices - Coding style, consistency, versioning, commenting, code reviews. All of these lead to easy to read and understand code that can be updated, debugged, or maintained by others.

Training - Staying on top of trending, latest, new technologies.

All of the above are done in and driven by and in partnership with the team's leadership roles, whether across the entire team, or as the technical lead.

Yes, I do agree with Deepesh, Influence, Emotional Intelligence, Conflict resolution, negotiation, group facilitation are critical skills for any leader. Here are some resources I would like to recommend:  Following thread will also give you good insight about facilitation: https://www.projectmanagement.com/discussi...ting-