I bit mine for 35 years. And when I say 'bit' them, I mean right down to the stumps, my fingers looked savaged and raw.
I managed to break the habit quite easily, which still surprises me. Here's how I did it:
I began by concentrating upon growing only two nails at a time. In my case I chose the 4th and fifth fingers of my left hand. More importantly, I allowed myself to still chew the remaining 8 nails to smithereens.
I did wear falsies on the bitten nails but would frequently chew them off. The falsies alone were no defense against my habit.
When the two new nails had grown (then snapping off, then growing again!) I then went on to grow two more, whilst still allowing myself to chew the remaining 6 to death.
And so on and so on until I had grown a full set of 10 'weak yet wonderful' new nails. It is disheartening when they snag and tear, but simple enough to just carry on, if you are determined.
I think this method worked for me because I didn't have to go full cold turkey all at once, and actually being able to compare the beauty of the newly grown nails to my ugly bitten ones drove me to persevere, one step at a time.
The urge to nibble is no longer strong, as in not biting them has become the new habit.