Nara
proper noun
Nara is good and it is Nara (the place, we're talking about).
なら
The reading for 奈 is good, the reading for 良 is pretty off in terms of what you've learned. But, if you know that the meaning is Nara, you know the reading is なら as well.
私は歯のしつこい着色汚れを奈良の歯医者さんで落としました。
I removed stubborn color stains on my teeth at the dental clinic in Nara.