I will try to answer this.
But I think M-GMAT has a special section addressing this very clearly. If you get a chance, review that. I don't have the book with me at the moment.
from GMAT point of view, make sure if there is a ";" then the sentence following ";" should be able to stand on its own. ";" is used in a compound sentences, combining to "independent" clauses. "Independent" is key.
As far as "like" and "as"
Use "like" when comparing nouns or pronouns , otherwise use "as" ( I think more precisely in case of verb phrase or noun phrase , use "as" )
then there is "such as" which is used to sight examples, as opposed to "like" where things are compared.