St. Paul tells us in Thessalonians to pray without ceasing. The older I get, the easier this becomes- I used to think that this was a very hard thing to do. I believe that the more we pray, the more grace we are given, and the more grace we have, the lighter the yoke -
Take up my yoke upon you, and learn of me, because I am meek, and humble of heart: and you shall find rest to your souls. For my yoke is sweet and my burden light.
Lately, I find that when I awake during the night, I think of someone from my past, and I am inspired to pray for them-even a quick Hail Mary before I fall asleep again. So now I carry this practice over into the day; often I will use a short prayer, such as -Lord, have mercy on him/her.
St. Alphonsus Ligouri, in The 12 Steps to Holiness and Salvation, says this about ejaculatory prayers:
St John Chrysostom says that he who utters ejaculations closes the door against Satan and prevents his constant annoyance with wicked thoughts. It is by acts of love, conformity and self-oblation, together with the invocation of the holy names of Jesus and Mary, that we give the greatest pleasure to God. One who loves, thinks constantly of the object of his love. A soul that loves God will therefore always think of Him, and seek occasions, alone as well as in company, to say frequently to your heavenly Bridegroom: "O God, I desire only Thee and nothing else"; or "I give myself wholly to Thee; I desire what Thou desirest; do with me according to Thy good pleasure." These few words alone are enough: "My God, I love Thee" or :"My Love, my All!" You may also, without uttering a word, raise your eyes to Heaven or cast a loving glance at the tabernacle or the crucifix. These silent acts are especially to be recommended because they require no effort, they can be more frequently made, and are often attended with greater fervor than other ejaculations. The best acts of love, of course, are those that well up from the depth of the heart at the impulse of the Holy Ghost.
The thing I like the best about these short prayers is that they are free of distractions, by which Satan robs us of the value of our prayers.