Probably best advice would be, find a publisher. Here is why:
As an example I will mention only two most common ways of "boosting" your game in Play or App Store
1. Paid promotions might be a good idea, but, you really need to be sure that your game will become viral, so you just need about hundreds of users to get hooked into your game and the rest will be spread with word of mouth. To get a big amount of users from promotion alone - you don't have that money.
2. Second choice is so called fake downloads. You are basically paying to some individuals/companies to boost your game with downloading it from different user accounts. These numbers will help your game just to have better download number and that's where it ends, you will get nothing else from it . To make it count you need to have a really, really big amount fake downloads - you don't have that money.
Reason why all these strategies will not work for you is connected with: publishers
Publishers, when they smell good game they are willing to invest hundreds of thousands in that game to promote it. The main goal is: game to be featured on appstore homepage. And how are they doing that? With 2 steps I mention above plus some additional promotion campaigns.
It's a simple math: Game to be featured in appstore needs to have really massive boost which is counted in downloads. Publishers are willing to buy (in whatever way) millions of downloads for that game to be featured, because they know that these numbers will multiply the moment they reach featured page. They invest thousands if not millions in paid downloads but at the end they get back what they invest trough monetizations from organic downloads (if their calculation was right that is) Of course there is retention that will dictate how much money game will bring, but that's another topic.
Please keep in mind, every time you invest some money into promotion or paid downloads you are competing with publishers that are investing millions in downloads against yours few hundreds/thousands. To make things even worse hundreds of publishers are competing against each other who will bid more for his game to be in top 100.
If your game is not somehow unique to become viral trough word of mouth, there is nothing more that you can do than to pitch your idea to publishers. When I started with mobile game development I fail deeply because I was not aware how cruel and unfair mobile market is, so please don't do same mistakes as I did and don't waste your money for nothing.