The only thing that will keep one from going to heaven, one who has reached the age of accountability, is for them to have never truly turned to God in repentance through faith in Christ Jesus as Lord and Savior.
As to your question about smoking cigarettes, smoking a cigarette has nothing to do with one's salvation.
A child of God (a Christian) should be aware, however, that God, through the indwelling Holy Spirit, lives within them. As the Bible says:
" Do you not know that your body is a temple of the Holy Spirit, who is in you, whom you have received from God? You are not your own; you have been bought at a price. Therefore honor God with your body."1
This being so, we should care for our bodies; we should not do anything which
would harm them.
The smoking of cigarettes has been proven to cause cancer, heart problems, emphysema, and death.
1 (1 Corinthians 6:19-20)