I'll just add typical "safe" use :)
- "более мягкий" → only БОЛЕЕ
- A horse is bigger than a dog → only "БОЛЬШЕ"
- 24 > 2.5³ → "БОЛЬШЕ" is way better (i.e., with things you can measure as a number)
- more than 200 people (больше, чем 200 человек) → БОЛЬШЕ is better, "более" is possible.
- over 9000, over 200 people (более 9000, больше 200 человек) → either is fine
- 'no longer' ("Я больше тебя не люблю") → БОЛЬШЕ is OK, БОЛЕЕ sounds quite bookish, but still possible ('Ты жаждешь того, чем более не владеешь'~'You yearn for that which you have no more').
In sentences like "Он ест только хлеб, и больше ничего" the word "более" is also bookish and not much used spontaneously.