Concrete marketing strategy depends on the niche and quality of the app/website
But in general, there are paid and free marketing tactics.
I'm good at both, but my stronger side is free or low budget marketing
I got no problems in spreading the word around with low budget (or no budget at all)
Also, thanks to previous website that I owned (sold it 1.5 years ago), I have significant amount of connections and mailing list/contact list with affiliates who can help promoting new stuff.
If your app/website can be promoted in each country separately, that's even better, since I also own a network of local marketers/promoters who can help bring any app to local marketplace.