<p>1) I spend two hours each day practicing swimming</p>
<p>It should be practicing to swim because "practicing" is a noun so a verb forum (infinitive) should come next.</p>
<p>Likewise,</p>
<p>2) we had fun pretending being rock stars </p>
<p>Being should be "to be" because pretending is a noun so a verb must follow it (being is a noun)!</p>
<p>Follow is rule:
Verb ---> noun ----> verb ---> noun ---> verb ...etc.</p>
<p>Good luck :)</p>