I think it’s best not to think about customer retention and growth techniques as “hacks”. Ideally your techniques focus on long term relationships with your customers where you provide great value, which is the best way to build a fast growing business and not lose customers.
Still, there are some common tactics for SaaS companies that can help:
Sign long-term contracts. If you have a month-to-month pricing plan, customers can choose to leave anytime. If they sign a 12 month or 24 month contract, they cannot churn for a year or two, which gives you plenty of time to change their minds. This is easier than you think, as you can provide an incentive (10% off) to sign a longer term deal.
Customer referral incentives. The best products grow because their customers become evangelists for them. While you can try to provide economic incentives for this kind of growth (credits, etc), what works best is to unlock a better product experience by adding more customers. For example, a billing processing service might be better if all the billers are also on the platform, which provides an incentive for companies to add all their vendors onto your product.
Invest in Customer Success. Customers might remember your product, but they will definitely remember how helpful your team was and how they made them feel. Companies often wait far too long to invest in customer success, since it can increase your customer satisfaction greatly and become a growth driver and churn reducer.