No, that's actually good practice. One shouldn't use an acronym (unless it's extremely common) without first writing it in full. However, it should be written out first and then followed by the acronym in parentheses. Like so:
Automated Teller Machine (ATM)
After this, the acronym may be used freely. But if you're just going to use the phrase once, you should just not use an acronym.
No, that's actually good practice. One shouldn't use an acronym (unless it's extremely common) without first writing it in full. However, it should be written out first and then followed by the acronym in parentheses. Like so:
Automated Teller Machine (ATM)
After this, the acronym may be used freely. But if you're just going to use the phrase once, you should just not use an acronym.