Momentum is the most important element in human productivity. They say that genius is 1% inspiration and 99% perspiration; I think that roughly 99% of perspiration derives from the sheer momentum that comes from bloody-mindedly doing something repetitively and consistently over the course of weeks, months, years, so that it becomes impossible to countenance missing even a single day.
It's like compound interest. Paying £50 into a savings account will get you nowhere even if it pays a 5% rate. Do it every week for a year and see what happens.
For a long time, I struggled - like, I suppose, everybody - with procrastination. I still procrastinate, of course. But I'm in a position now where it is just a mild source of guilt, rather than a crushing, debilitating disease like it was in my 20s. What made things click was doing a PhD. For about 9 months, I sat down and wrote every single day, because I had to. For the first couple of days, this was difficult. But soon enough it became difficult to imagine not doing it. The habit became ingrained and then it was like riding a wave.
The relentless force of momentum is necessary for completing any project of any worth. You have to get over that initial period of inertia, during which almost literally anything - tidying your desk, cutting your toenails, watching old YouTube clips of Gary Neville ranting about David de Gea's goalkeeping, looking at random articles on Wikipedia - seems more attractive than what it is your are supposed to be doing. But once you're past that, you're in the clear blue sky, and you are flying towards your destination, and almost nothing can bring you plummeting back to earth.
This is also true of exercise, of course, and learning any sort of physical skill; doing 30 push ups one day is pointless unless you are going to do that again and again and again, three or four times a week, and then build up to 40, and 50... Until you start to feel weak and diminished unless you stick to your schedule.
But it's also true of gaming. As a grown adult with a job and family and other responsibilities, it can be very easy to set up a game that gets together only every other week, or once every three weeks, or once a month. And it can then be very easy to miss a session, because Bill has to babysit and Jane has to do a work thing, so that it ends up becoming even less frequent than that. Momentum can dissipate before it even gets started - and the result is then, let's face it, often a shit campaign. People forget things, they lose energy and enthusiasm, and they simply lose that feeling of connection with their characters and what is happening in the game. Things begin to seem attenuated and distant - and then it becomes easy to cancel next week's session, and then the next... In On Writing, Stephen King says that if he is working on a novel he simply has to write it every day; if he misses one day it will not be utterly fatal, but anything more than that and he simply loses the thread. The characters stop seeming real and the emotional connection dissipates. A D&D campaign has something of this quality too; you don't need to play every day, but you need to do it regularly enough to stay in the zone.
What this points to is weekly sessions that you run come hell or high water. This is what I've been doing since February, week in and week out, and it works. And there is time to do it, if you take the thing seriously and stop the ridiculous excuse-making that afflicts all of us: "Sorry guys, I have to cancel this week because..." Run a weekly game for five sessions and the prospect of having to cancel one week starts to feel painful. Run it for 10 sessions and it begins to seem unimaginable. And that's how you reach the sweet spot and can start to really shift up the gears; that's how you reach the promised land of a campaign that generates material of its own; that's how you get really satisfying play. You just have to get the momentum going.