I don't know where the expression "practice makes perfect" derives from, but I wouldn't be surprised if it were the Bible. The Bible has a lot to say about practicing righteousness, and a lot about aiming for perfection.
In the mid-1500s, the expression was found in the form "Use makes perfect" (Latin: Usos promptos facit). That reminds me of a passage in Hebrews:
"For though by this time you ought to be teachers, you need someone to teach you again the basic principles of the oracles of God. You need milk, not solid food, for everyone who lives on milk is unskilled in the word of righteousness, since he is a child. But solid food is for the mature, for those who have their powers of discernment trained by constant practice to distinguish good from evil" (Hebrews 5:12-14).
The Apostle John talks a lot about "practice." He says we need to "practice the truth" (1 John 1:6). Evidently, it is no good just knowing the truth if we don't practice it.
John says three times within a few verses that it's no use saying you are one of Christ's if you don't "practice righteousness" (1 John 2:29; 3:7; 3:10).
I don't know exactly what the old timers meant by "practicing the presence of God," but I think John means really "practicing righteousness" in the modern way that we mean the word, of creating a habit. We saw in the Hebrews passage above that practice makes perfect. Training in obeying God makes perfect.
This is especially true in the area of spiritual warfare. When we are tempted by some wayward temptation in the course of a day, to say or do something that we know would not be pleasing to God, it is all too easy to give in and to reason that after all we are weak and that God knows we are weak and will forgive us. But why not rather "practice the truth," as John says, and repel the demonic prompting with every fiber of our Spirit-filled selves?
We may find, after doing this a few times, that it gets a little easier, because we have established a habit of righteousness, a holy, well-worn groove. And hope rises, because after the first battle's won, we know personally that it is possible.
Practice makes perfect.