The best way to disciple is to do it how Jesus did it. He dedicated Himself to the constant care of 12 disciples who would reflect His character and follow His footsteps to take the gospel to others.
Now it came to pass in those days that He went out to the mountain to pray, and continued all night in prayer to God. And when it was day, He called His disciples to Himself; and from them, He chose twelve whom He also named apostles.
Luke 6:12-13, NKJV
We need to focus on discipling 12 because that's what Jesus did. The Lord chose them and intentionally kept the group small with the purpose of being able to carefully work on each man's character. Many could follow Him, like the 70 in Luke 10:1, but Jesus focused on discipling only twelve.
Jesus deliberately chose to dedicate Himself to preparing this small team because He knew the principle of pedagogy that the smaller the group being taught, the greater the chance of effective teaching.
The Teacher dedicated more than half of His ministry life to forming this team. He literally consecrated Himself to teach them through His example and later sent them out to fulfill small responsibilities under His supervision.
That is why we understand the anguish Jesus felt for them in John 17:12-15 when He prayed for His disciples. Jesus asked the Father to guard His team in the difficult moment they were about to experience.