I generally don't like to link to slides, since they miss a lot of substance that is present in a real presentation or in an article, but this one by Sean Johnson is pretty excellent. Click through for a solid guide to customer growth with many useful and actionable tips and bits of information, such as this 90-second guide to Facebook Ads:
Images are the most important factor. Test 50 images. Test orientation (looking right, looking left). Test colour and shape of borders.
Use country targeting when testing conversion. US costs 5-10x other countries. Use Canada, New Zealand, etc.
Focus on conversion, not just on clickthrough rate. It's not uncommon to have 40-60% conversion rates if it's targeted well.
The guide is shallow, but provides a good overview with lots of starting points and links to further information. Worth a read through, and some clicks.