"But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control. Against such things there is no law." NIV translation
Fruit grows automatically on a tree and the type of fruit produced depends on the type of tree. The same type of thing is true for people in that our actions will display the state of our relationship with God. If we are led by the Holy Spirit, then, we will display this list of characteristics in ever increasing measures. It does not depend on our efforts but is just a natural part of our life and walk in the freedom of the Lord.
This verse has been misinterpreted and many Christians have wondered why they still do many of the things that they did before they came to salvation through Jesus Christ.
Crucifixion was not a sudden way of dying; it was quite the opposite as it could take quite a bit of time for the victim to actually stop breathing.
It is much the same when we think of "crucified the sinful nature"; putting the victim (sinful nature) on the cross is the first step. In God's time and through the power of the Holy Spirit, the breathing (passions and desires) will slow and finally stop.
"Since we live by the Spirit, let us keep in step with the Spirit." NIV translation
One of the first things that you learn when you join the military and go to basic training is how to march. Marching is basically walking as a group and this is done by everyone moving in the same way at the same time. This eliminates confusion, crashing into each other, and falling down. The key to marching is rhythm and someone that is put in charge to call out the steps. This is also true of the Christian walk and the One who is to call out the steps is the Holy Spirit.
"Let us not become conceited, provoking and envying each other." NIV translation
Pride is what caused Satan to be cast out of heaven and it is at the root of many sins. Paul reminds us that walking in freedom is also walking in humility because we are not free by our own efforts but by the grace of God. A common pride issue is when so-called "super Christians" begin to look down on others that are not walking in the Spirit. We must accept others where they are and help to lift them up to what God has for them.