I'm not "long" perse. But i retained every inch of growth for two years while I transitioned to natural. I was apl when I started my transition and I was apl two years later. Now I'm below my shoulder blade. Unlike some transitions, I didn't have to cut all my hair off. Which for ME was major.
Keys for me:
Deep conditioning on schedule. Not being lazy. I deep condition once or twice a week and use deep protein regularly to fortify my hair.
Trim ends as needed to minimize or eliminate breakage.
Protect my ends
Use heat very sparingly
Moisturize regularly with something...water, products, something!
Protect my hair at night
Use products that work for my hair and don't veer off to the left on bandwagons and trying new stuff
Taking my time with my hair. Not rushing, not stressing, not ripping at my hair when I'm frustrated or bored or worried about "her"