Make schmooze calls!  Yes, pick up the telephone just to call and say hello.  They'll ask you how business it at some point, but keep it a schmooze call. 

Picking up the phone is important.

Personal contact is important for your soi

In my opinion, Phone calls, a quick hand written note, or face to face conversations are the best ways to keep in touch with your sphere of influence.

If they are out of town contacts, then I would send a handwritten note with a piece of valuable information pertaining to the market in their area or just some helpful household tips.

My SOI are people I volunteer with and people on my personal Facebook.  I've gotten several clients through both.  I had a pool home for sale I shared on my personal FB, one of my friends commented about how they would love to have a pool home, I said "I can make that happen."  A month later after they talked with a lender, I showed them homes, they had an offer accepted on one and I listed their place.

Regular contact.

Listening throughout the transaction, and committing things that are important to clients.

This week, since so many like Pumpkin Coffee, I bought some and just drove around and dropped it off  to clients, preferably at their workplace.  Words wonders.

Be personable, not mechanical or systems oriented when seeking their influence. A phone call, email, invitation or a handwritten letter will tower over any drip campaign generated through software. You're wanting to touch that person or someone they know who can bring business your way and not just invite them to look at your website.

Constant contact with emails and calls.

I did effectively use Top Producer for many years. I am not up to date on the best alternatives and that would be a good blog topic for you.

Keep in touch some way at regular intervals.  Client appreciation parties also do wonders.  Any software with a planner should be able to handle this.

I do send birthday cards, but often send emails or pick up the phone to make personal calls to my top A+ clients that refer lots. 

It's a big time investment upfront but if you invest in a real business CRM like InfusionSoft and set up all the campaings and emails yourself it is a great way to automaticlly sent out birthday emails etc and stay in contact. You can customize when certain task happen and if they take a certain action in an email they move to a different campaign, it can get very complex.