Begin with tan (as), and add the adjective or adverb.
Dolores es tan conscienzuda (Dolores is as conscientious)
Ella estudia tan diligentemente (She studies as diligently)
Add como (as), and complete the rest of the sentence.
Dolores es tan conscienzuda como Jorge. (Dolores is as conscientious as George.)
Ella estudia tan diligentemente como él. (She studies as diligently as he does.)
If you want to make a negative comparison, put no before the verb.
Tú no eres tan trabajadora como él. (You are not as hard working as he is.)
Tú no escuchas tan atentamente como Juan. (You don’t listen as attentively as Juan.)