The best thing is to check out Shopify’s marketing guide called 50 Ways to Make Your First Sale – it is full of tips and marketing ideas to Boost your store.
Apart from that i would recommend
Build Content Strategy based on your Customer Persona (Target Audience)
SEO and Social Media always gives long term return and its worth investing if its targeted very well
Some of the Marketing Apps you can use form Shopify App store for example Loyalty, Reward , Instagram follower app etc
Even you check with Kit, lot merchant uses very well you can check out their videos and functionalities. Kit can now create Dynamic Product Ads that retarget shoppers on Facebook who left your site without purchasing. You can find a step-by-step guide here on how to use Kit’s retargeting features and I would definitely recommend setting this up for increasing your sales.