you are on the right track mate,

i have been working with apps for over 4 years, and only recently been working with paid advertising - there is a lot you can do for free marketing - just google it, and keep trying and learning - this is great learning tool for understanding the entire App market place

dont let the lack of funds stop you - i built everything with nothing myself also.

Just focus on this

Your app is your business - your product.

Your active users are your customers - when a customer uninstalls your app you have done something wrong - and have lost a customer.

Focus on the quality and service of your app.

Once this is perfect then you can worry about marketing - u dont want to market a product that doesn't work well.

Start a blog - talk about your experiences, what you are working on the app, get people involved, have a beta test group for testing out new versions, work on your play store keywords.

Analytic are good for dissecting each parts of your app - just like any business - treat your customers well and with respect and you will get it back.

All the best - the app game is not an easy one but as long as you take it seriously, you will outperform most apps by a mile. As really most are just devs trying to make a living by flooding the market with cheap apps, so quality always outperforms