That key is really no secret at all. It all comes down to consistency.
Have a marketing plan. Follow it consistently. The end result? Plenty of leads in your sales pipeline.
Have a sales process you follow. Accomplish sales tasks every day, consistently. End result? More closed sales which means more revenue.
Have a client relationship management (CRM) program all spelled out. Follow it consistently every day. End result? More "low hanging fruit" business from existing clients, more referrals and more revenue for your business.
So the big secret key that everyone is searching for is really just consistency.
It doesn't matter what form of marketing you're using, what system of selling you prescribe to or how you keep track of your client contact activities.
All that really matters is you have a plan for marketing, sales and CRM and follow it, yes, that's right, consistently.