Look some good marketplace beside apple store and choose some attractive and catchy name for your app to attract your target customers and then grab your social handles especially facebook twitter and snapchat and post links to your app alongwith some unique description. Tag your app correctly to your social links and make use of your own social connections to enhance the outreach of your app.

You can also offer some free beta downloads to get some initial reviews for your app and as a next step you can offer these free downloads to some tech blog writers who can write a blog on your app that will not only establish the credibility of your app but will be helpful in rapidly promoting your app.

You can use google analytics to measure the analytics of your app.