Devout and recollected, we should think of the Lord Whom we are receiving, and make fervent acts of virtue.
In approaching the communion rail one should have his hands joined, and not walk too hurriedly, nor rush ahead of others, nor insert himself between two persons already kneeling close to each other at the rail. It is very irreverent for women and girls to go to Holy Communion with sleeveless dresses, low necks, and no stockings. The paint of their lipstick may possibly touch the Sacred Host.
***When the priest approaches, one should raise his head and open his mouth, with the tongue slightly extended over the lower lip. After Communion, he should withdraw to give room for others, and return to his place with joined hands and downcast eyes.
One should swallow the host as soon as he can. Jesus stays with us only as the appearances of bread remain. If the host sticks to the mouth, we must on no account remove it with the finger, but moisten it with saliva, and remove it with the tongue, then swallow it.
Source: My Catholic Faith