In The Small Catechism, Martin Luther suggested that Lutherans make the sign of the cross both in the mornings and the evenings when we pray.
Doing so helps us to invoke the names of the triune God of all creation--Father, Son, and Holy Spirit--over our waking and our sleeping.
It also helps us to remember the covenant God made with us at our baptism. This is a huge comfort to me as when, Luther says elsewhere, the devil makes me doubt that Christ really has covered my sins. Under those circumstances, I can shout to my doubts and that old liar, the devil, as Luther did, "But I am baptized!" This reminds me to trust in the God Who sent Jesus to keep claiming me as His own as I turn from sin and entrust my life to Jesus! No matter how I feel at any given moment, I can trust that the Lord Jesus to Whom I cling for life is working for my good and is good for His promise of eternal life for all who believe in Him!
I like this little step-by-step illustration of how to make the sign of the cross from a blog called Pastoral Meanderings. (I love how 1940s the illustrations are! It reminds me of some of the pictures that were in The Boy Scout Handbook back when I was in Scouts.)
There are a surprising number of variations on how Christians cross themselves, though. So, if you don't do it exactly as it's illustrated here, it's no biggie. And your salvation won't go out the window if you don't cross yourself, of course. But, for the reasons listed above, it can be meaningful.
After making the sign of the cross, I always touch my heart three times, again "in the name of the Father, Son, and Holy Spirit," expressing my love for God, doing so after I receive Christ's body and blood in Holy Communion. (Or, on those rare occasions when I'm blessed to be in the congregation worshiping as someone else leads the service.)