Every page on a website is an ad for the next page
A page fails when it doesn't convince somebody to click to the next page. Fix the pages that fail most often.
Make your download and app flow seamless
People now expect to get to your service before a transaction (like signing up) is needed
If you find an idea that works, iterate on it like crazy
Iterate on it until you can't anymore.
Everything is an experiment.
Test everything. Look at the results. See how you can improve them.
Customize experiences by country
Each country has a different behavior and culture. Your product will need to reflect this.
The future of signups?
Phone number signup and passwordless signups (like Touch ID)
Prioritize your highest traffic opportunities
Eliminate things that don't add value and use any data you can to run experiments.