Caveat: you may or may not feel comfortable with a motto with religious background, but the concept we have today of a leader as a servant has had a strong influence from Christianity, so personally I don't see any harm in using it even if you/your club is not religious at all. Moreover, there is precedent of this specific motto being used by non-religious groups
Non ministrari sed ministrare (Mt 20:28)
Literally means [I have come] not to be served but to serve. The context is Jesus explaining his disciples that anyone who wants to become great among you must be [each other's] servant (Mt 20:26.) This is the base of the western concept of exerting leadership/power by serving.
It has been the motto of a number of educational institutions from different, Christian and non-Christian backgrounds (e.g. 1, 2, 3, 4) and at least one bishop (presumably more.)
In Spanish it is common to call a country's President Primer Mandatario (something in the line of first mandatary/trustee, first one being mandated, even at the point that mandatario has kind of lost its original meaning and is at times translated as leader.)
Most Popes, as well as some Western civil rulers have considered themselves servants at the point of coining and using the title servus servorum Dei (servant of the servants of God.) Of course some have used the title just as a formality but also some have trully meant it.