The Charity Commission explains what it means to act in this way, and how to avoid making common mistakes.
How do you make sure that you act in your charity’s best interests? It’s not about protecting your position as a trustee or even the jobs of all your staff. It’s not really about preserving your charity forever (although planning for the future is important, of course). It’s about doing the right thing.
It really means doing whatever you and your co-trustees (and no one else) decide will best enable the charity to carry out its purposes, to make sure that you’re delivering the best possible benefit to the people that your charity helps.