Great that you are already getting recommendations from happy customers. That is the best source.
I assume that you have links back to your company on the websites you design. Most website designers do but I have seen some who don't which always seemed to me to be strange.
Second, after you have designed a website for someone do you offer any follow up services, perhaps a quarterly or six monthly review to make sure that things are up to date. It is very easy to still promote an event that happened four months ago but it gives a bad impression to visitors.
SEO advice is another ongoing service that you could provide. I still see so many websites that commit some of the most basic
SEO errors. It is not difficult to get good positions for local searches if you tick the boxes and most small companies only trade locally.
Incentives for referrals are an interesting situation. Some people like it but others hate it so it depends on the person. It may also depend on your incentive. A £50 thank you and reduction off your future fees is likely to be seen differently to a £50 cheque.
You do say thank you when you get a referrals don't you. It is essential to acknowledge and if possible have some kind of reward, even it it is an after the fact box of chocolates or other small item. In reinforcement theory you get more of what you reward.
I thought I had contributed to this post before but perhaps I forgot to press submit. I won't make that mistake this time.