Question: “I want to be baptized by the Holy Spirit, how do I really fast, what should I do when fasting.”
Answer: Your questions are important, but I need to make sure I understand them properly. It appears you may be conflating baptism of the Holy Spirit with fasting. Baptism of the Holy Spirit happens upon the moment of salvation. If you are seeking to be baptized by the Holy Spirit then you must place your faith in Jesus Christ’s death, burial, and resurrection as the fully satisfactory payment for all your sin. This is salvation! Holy Spirit baptism is not accomplished via fasting. It happens upon the moment of belief in Jesus Christ for salvation (Ephesians 1:13-14). This permanently places you into the body of Christ (1 Corinthians 12:12-13).
Jesus spoke of this event in John 7:37-39. Be careful to note when this baptism would occur.
“But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.”
Fasting is the denial of food to engage in spiritual exercise like prayer with greater concentration. It is not related to salvation or to receiving the baptism of the Holy Spirit. Fasting is a good practice for believers from time to time to increase their concentration while in prayer. I am not sure how to best practice fasting, but it is wise to adhere to Jesus instruction in Matthew 6:16-18 and avoid falling into the classic attitude of pride. Fasting isn’t something we do to punish ourselves or make ourselves self-righteous, either. I hope this helps!