Yep, the great secret to missionary work is work.
As I have been working in the Lord's vineyard, I have discovered that hard work is something that is difficult to do. It's almost a habit you have to make, and some people never really catch onto it.
I'm not saying that to point fingers - there have been plenty of nights where I have laid down and thought to myself, "Man, there's a lot I didn't do today."
The best way that I have found to motivate myself is by doing a nightly inventory with God. My workdays improve as I kneel down at night and ask myself this question - "Am I better now than I was this morning?" There have been plenty of nights when the answer has been no, and there have been a couple of great nights when I can definitely say yes, but more often than not, I find myself saying, "Lord, I don't know if I'm a whole lot better, but I've tried my hardest and I felt the Spirit working through me today."
As we work hard, it is easier to be obedient and to love every aspect of the work. If you keep on that path, before you know it you'll be an effective missionary - a consecrated missionary. That's the missionary I want to be, and I'm starting today :)