As a marketer with many years experience in the digital/social/online space, I'd thought I'd chip in my 2 Satoshi worth too.. (Since this topic is still alive)
Firstly, its all about the product and who its potential audience is..
The product and the market will determine the strategy you choose, so it firstly depends on what you're selling and who you want to sell it to.
ie: Is it a pump-and-dump product that you just want to flog? (Such as affiliate products, referral links etc)
Or is is a product you care about and want to nurture for the long run? (Something you developed yourself or want to stick with/grow)
If its something you're going to stick with for the long haul, then as some people have already mentioned, building a good blog site and getting all the appropriate social media in order is absolutely essential. You'll also want to take advantage of services line Mailchimp, ShortStack and Landing pages to grow your mailing lists and maintain ongoing, meaningful communication with the audience. (newsletters, competitions, special offers, giveaways).
In that universe, Social Video is king right now, so make sure your blog and socials are filled with plenty of interesting, up-close-and personal video content. Even if you don't like being in the spotlight yourself, you can easily create heaps of short videos of people using your product, giving it a review etc. Social Media algorithms love video right now, so use that to your advantage.
Facebook/Instagram ads as well as Adwords are a really cost-effective way to compliment your efforts and help drive awareness to your product too. Facebook is now geared in a way where it is very difficult to build big page organically, so it is definitely worth spending a bit on 'sponsored posts' and PPC ads. You can get results here for as little as $50 a week and simply grow your budget as you can afford to.
Also think of other advertising platforms that may be specific to your product - Eg: Coinads, Mellow Ads and the like are great for promoting products within the Bitcoin/Crypto/Digital space.
If the product/brand is something you care about, never use annoying techniques like pop-ups, spamming etc. People will just view you and your product as annoying and probably not credible so definitely spend the time developing your audience instead.
On the other hand, if its just an affiliate product you want to sell, you might not want to go to the effort of setting up a blog or socials.
You can easily market affiliate products without any of that, simply through Adwords and other PPC ad platforms.
Anyway, there's a start!