Peter replied, "Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of you sins. And you will receive the gift of the Holy Spirit.

One time, my sister was given a glass of water and syrup by her teacher. Since the solution wasn't stirred yet, the syrup stayed beneath the water. My sister drank it and said it tasted plain. Then she took a spoon, stirred the syrup and drank it. It tasted great! Sweet!
The glass of water represents our lives while the syrup illustrates the Holy Spirit. Every time we get ourselves baptized and accept Jesus as our Savior and King, God will give us a gift which is the Holy Spirit.
Repentence means sterilizing our hearts so that the Holy Spirit can enter into it. Just imagine how the Holy Spirit stay in us if our hearts are full of sins! There would be no place left for the Holy Ghost!
However, nowadays people who are already baptized (including us) aren't reflecting Jesus in themselves! How could this happen!!?? The thing is they have not 'stirred their syrup and water' yet!
When we give ourselves to be led by the Holy Spirit, our lives will change! I'm not saying that our problems will be gone, what I'm trying to say is that the problems  we face are still the same, the only thing different is ourselves. We have the Holy Spirit Who will tell us things we must do and musn't do. The Holy Spirit will always guide us to the Truth.
Next, how do we know if we're activating the Holy Spirit or not? 1) Pray regularly. Prayers are the most important conversation of the day. 2) Read the Bible. The Bible is the Bread we have daily, not the cake we have occasionally. 3) Obey the Bible. Remember, words will be just words until we bring them to live!
Actually, I have this little habit of asking the Holy Spirit to do things with me. For example, I want to study then I'll say, "Holy Spirit, lets study!" in my heart. Even when I want to take a shower I ask the Holy Spirit too!
Let me just say that things done with the Holy Spirit are always fun and full of joy! Though some things aren't that pleasant or don't come the way we expect.
So, lets dedicate our lives to Jesus and ask the Holy Spirit to guide us in everything we do!
Holy Spirit, please lead us always! Amen!