Don't A/B test until you have thousands of daily users/visitors. Otherwise meaningful results will come back after months and that is way too slow.

Avoid low-impact, low-effort work. "I just takes a couple of hours" is a common reasoning for this kind of optimization. Time spent easily compounds and then you only do all this low-impact stuff, never achieving anything. Focus finding high-impact, high-effort work like content marketing.

Establish partnerships. Partner up with other companies that can direct their customers to you without losing any revenue. You may also consider using other products to promote your own. Do not start a partnership with a direct competitor.

AirBNB integrated with Craigslist.
Gave option to also post notifications to Craigslist.

Promotional swap with other companies:
- Swap social media updates.
- Swap a mention in internal emails to users.

"I would love it if you could tweet [insert link] to your followers.
Let me know if you need a tweet.""

Embrace the dark side. Make Internet hate machine to work as gears in your engine of growth.

• Find subreddits, forums and image boards of your target audience. See what they are discussing and join the discussions. Avoid being openly biased.
• Create memes and similar content. Even offending memes are good if they are funny. All publicity is usually good publicity.
• Find who are linking to your competitors and get them to link to you.
• Find people that are influential to your target audience. Book an interview with them.
• Use online tools to search potential clients to follow e.g. Followerwonk.
• Hashtags are usually just noise but great to use for promoting yourself on conferences when you are not in fact attending.

Consider seed supplying your content. Create generic, creative-commons licensed content and content with attributions. Stop when you get your fair share of customers.

Reddit created fake profiles in the early days to boost up growth.

Sources

• The Growth Handbook, Intercom