'Like' v/s 'As'

The rule is very simple - Since 'Like' is a preposition and 'As' is a conjunction.(click here to read what are Prepositions & Conjunctions), use 'like' to compare nouns and 'as' to compare clauses (click here to read what is a Clause).

Examples:

1. John & Jacob, as/like their father Mark, are excellent players of cricket.
   
   In this sentence John & Jacob are nouns that are being compared with another noun Mark. Hence the correct word here is 'like'.
   
   
2. Just as/like reading is good for the mind, running is good for the body.
   
   In this sentence two clauses 'reading is good for the mind' and 'running is good for the body' are being compared; so the correct word is 'as'.