At MPBC we've just started using this resource to hold each other accountable. It's a very thorough two page pdf form that a few of us complete and then send to each other every week.
Accountability gives us the opportunity to be honest and real about the sin we struggle with. It cultivates humility as we confess our faults to each other. It helps us to pray specifically for each other encouraging us to be the church that God has called us to be.
Other benefits of accountability from Andy Naselli:
Motivation: It is an added incentive to glorify God with our whole beings in very specific areas, including our minds, bodies, families, and time-which all belong to God (cf. 1 Cor 6:18-20).
Safety: It is a safety net. If one of us starts slipping or falls hard, two other concerned Christians are right there to catch him or pick him up with biblically informed advice and love.
Consistency: It facilitates (but does not automatically result in) consistent spiritual growth.
Specificity: It requires specific answers to specific questions. If someone asks “How are you doing?” it is very easy to cover up areas of our lives by blowing smoke about something else that may not be as significant.
Thoroughness: It holistically challenges us in multiple areas, rather than focusing on just a few.
Community: It establishes intimate, healthy relationships with fellow believers, rejecting a lone-ranger mentality.
Intensity: It encourages us to maintain a higher level of intensity. Although we may hold different convictions regarding the application of the gospel to lifestyle issues, we can identify with John Piper in his answer to Justin Taylor’s question, “What about your approaches to pop culture? Pastor Mark [Driscoll], you go to movies. You watch TV. You listen to modern music and go to comedy shows. Pastor John-you don’t! So John, how do you stay relevant by mainly avoiding pop culture? And Mark, as you take part in pop culture, how do you stay faithful and transformed rather than being conformed?” Piper replied, “My short answer is that I think I’m weak and therefore would probably become a carnal person if I plunged more deeply into movies than I do. That’s the first answer: Piper’s weak; he has to steer clear of certain kinds of things in order to maintain his level of intensity” (The Supremacy of Christ in a Postmodern World, ed. John Piper and Justin Taylor [Wheaton: Crossway, 2007], pp. 152-54).
Reminder: It is a constant reminder of what is eternally important, and it cultivates a mindset that we live in between Jesus’ two victories, which parallel D-Day and V-E Day in World War II: a decisive battle (i.e., Jesus’ victory at the cross and empty tomb) has determined the war’s outcome, but one final battle remains to end the war (i.e., at Jesus’ return). We confidently expect that God will restore and consummate all things for His glory and our good, and until then, we struggle and yearn for that consummation while living for another time and another place (cf. Rom 8:17-25; 2 Cor 5:1-10; Col 3:1-5).