Top three recommendations :-
Provide customized discounts and perks for members depending upon their profile like most travelled route,during what time of the day they use the service the most,average ridelength etc.
Encourage casual riders to signup to the service by providing discounted monthly/yearly subscriptions or providing addon services.
Incentive riders who travel during less busy hours or travel on less popular routes so that more riders opt for our service.
Start referral programs for existing users so if someone joins using their referral ,existing user gets ride credits which they can use for their next trip.
Encourage users to share their experience with service across all social media platforms.