Run whatever you are thinking in one country - most big games used to target Canada first (similar to U.S.).
So you can do a run with Canada.
As you may know Google Play rankings etc. work individually by country (as if they are parallel universes) - this suggests the much mentioned “first month” is different for each country - so I THINK you should be safe - i.e. releasing first in Canada may not harm your first month (later) when you push to U.S. (maybe someone can confirm).
Google gives you one month - you have an excellent opportunity to reach “Top New Free” in that time - your challenge is to leverage that early success to continuing exposure.
You could BUY reviews on the web - most developers here say negative about that (partly because who reads the web - it’s 1/10 of the mobile audience). However having multiple websites linking to your website etc. MAY give you some ranking boost (at least on internet searches).
Make a youtube video - that itself wil give you a good number of downloads - interact with people on youtube via your videos, twitter, facebook etc.
We had a discussion here about how to spend - and one suggestion I gave was to perhaps spend in a RISING trend i.e. spend at an increasing rate (as long as you have money).
So watch the daily downloads and for next day schedule a spend that is say 50% of that or 25% of that - i.e. goal being to “supplement” the natural download rate.
Optimize your description, esp. title (you have limited characters - choose words wisely) - some use Adsense keyword tool website to gauge the value of the keywords.
Maybe think about advertising in “similar” apps - as that demographic will be more likely to install your app - and retain it.
Prior to launch of your app - maybe create some pent up demand by publicizing first - or “coming soon” webpage (not a huge impact - but may have some impact).
I am no expert - but this is all free advice Experts will charge you for that advice - and their advice may be good or may not.
From comments here - response from admob advertising was criticised - but via AppBrain was praised i.e. $0.20 typical bid for downloads of your app. However as soon as you stop spending you will lose that source of dowloads - which will make you fall in rankings (and be classed as a “downtrend” by Google) - so you need to have ways to have second, third stage of rocket start after the first one fizzles out etc. …
Hopefully your app will be “viral” - will fill a need - will match search keywords (so just get downloads from search).
Note that putting too common names in your title (just because are commonly searched) MAY NOT help you - for example “file” is often searched - but if you put file in your title - that DOES NOT DISTINGUISH your app - I have seen cases of apps whose developers complain here that their app is NOT SEARCHABLE even when you type the title exactly !!! I have confirmed this happens with some apps - and I suspect the reason is that the title words match OTHER apps much more - so first 200 apps are those apps.
So if you call your app File Audio - users who type File Audio will find results that match ALL the other file related apps which already have high ranking etc.
So in a way you need to find words that are good for search BUT the name of your app is distinctive enough - so when people mention your app to others - it is FINDABLE.
So the name being unique helps in that - maybe make sure there are few possibility of spelling variations of the name etc.