我(也)很好 and tone sandhi
Looking at 我很好 this falls into the "When there are three 3rd tones in a row"

The 我 is one syllable so it falls into this part:


  If the first word is one syllable, and the second word is two
  syllables, the first syllable becomes half-3rd tone (˨˩), the second
  syllable becomes 2nd tone, and the last syllable stays 3rd tone


For this 我也很好 this is logically split like this (我也) and (很好) which would result in two lots of 


  the first syllable becomes 2nd tone (˧˥), and the second syllable
  becomes a half-3rd tone (˨˩)


At least that's what the rules say. As per my comment above, don't bother memorizing this. It is more likely an incidental phenomenon as a result of regular use of the language. In other words, you will pick it up by learning to speak it fluently rather than trying to learn it from paper.