I actually tried the cold-email bit only once. The response did not impress me positively. But that was in the last century. Maybe a should give it another go...
My personal marketing relies a lot on referrals and repeat clients. I used to participate actively in LinkedIn forums, but then got really busy and had to stay away. I am slowly getting back into the groove. Tools such as Buffer and Hootsuite help.
Nowadays, I use Canva to create nice looking introduction cards and that is what I send to existing clients, potential clients (people who I have met on conferences and networking events I attend). Those are set in a way that they can be easily forwarded as a referral intro, if need be.
Going back to your question, I do my buttering up in person, then send them a nice looking "invitation" to contact me. I am currently designing one. I can place it here if it is ok.