The most obvious change in strategy is to double down (for free) on 9, 10 or l1 against any dealer up-card. Likewise, you'll want to split (for free) on any pair except 4's (against 5 and 6 up-card only), on 5's (free double), and on 10's (don't split).
When a free bet wins, your sportsbook will only give you the profit from the wager and not the stake. This is known in the industry as a Stake Not Returned (SNR) free bet. Whereas your successful real money bets will see your profit and stake returned to your account.