Ok, I see what you are wanting.
For that, you need to create work that is so unique and inspiring that they feel compelled to boast about it via social media and too their friends.
Gifts etc. are not the way to go, not unless your clients are getting gifts of things like washing machines, holidays or car etc. It will get treated like junk mail and binned, or put somewhere to gather dust and never be spoken of again.
I had one referral this year who booked me, because they didn't realise I was at their friends wedding, which they attended! Until after the pictures were put on facebook. They loved the pictures, but loved the fact that we were practically invisible even more.
Another from a couple who I haven't even photographed yet, just because they felt so at ease during their consultation.
I have seen people giving money to clients who refer them, but they are just recommending for the monetary gain as soon as you stop giving away money no one will bother. It also won't attract the clients you actually want to deal with stylistically.
Typically clients will post things on facebook, pinterest etc. and that will be the end of it, they won't go round telling people to hire you, but if they are asked they might recommend you. That's the most you can ask for.
You are offering a service, so that has to be pleasant and efficient. And then offering a product. That has to be presented professionally and the contents to the standard they expect if not beyond them.
If your after care is full of gifts, treats and messages, then your client might start to feel pressured or semi stalked, and that will work against you, undoing all your previous good will.
You also can't expect referrals from every set of clients, I have done plenty of weddings where the couple might be getting married for the first time, but every one else there is already married. In that situation any "chatter" would just result in people wishing that they had found you for their wedding 5 years ago!
Referrals might take years to come back to you, a couple you photograph in 2014, might have a few single bridesmaids that meet someone in 2015 get engaged in 2016 and because 2017 is an odd number, decide to get married in 2018! But if you are lucky they will of liked your photo's and ask the previous bride who you are and then they book you 4 years later.
This is a long game, which is a hard concept in this age of instant gratification. Besides if you work hard for your success you get to appreciate it more when you finally make your endeavours work.