Next, I experimented with very low budgets for my own websites.
After that, small business for family friend. It all went surprisingly well and wasn't that hard, really. You just need to be very data-driven and methodical.
Game changer for me was NGO and Adwords grant (https://www.google.com/grants/), which gives you $10 000 per month. You can experiment without fear, trying everything you read or thought about.
When you optimize campaigns and grant limitations are starting being annoying, that's when you are ready for the real big work.