In this context, a complex task is defined as one with multiple steps over a long time period, and one where the one(s) in charge don’t necessarily know everything about what’s coming over time. A classical development project, if you will.
The most important action before even starting on the task is admitting that it is a complex one. Also, it is good to admit that you cannot foresee all of the challenges that will come up over time, but that you are 100% determined to pull it off.
Also, you must review the objective of the task to know when it’s completed. For instance, when are you finished “learning to play guitar”? This “goal” is so abstract you’ll never reach it. So you may want to “learn to play guitar as good as Steve Vai”. That’s a bit better, but unless Steve Vai is dead he’ll progress too. So you may end up wanting to “learn to play guitar so good I can play all Steve Vai songs”. See? Now you know when you’ve reached the goal.
Next, you need to find personal support. This means not only do you need a trainer or teacher, but also a sparring partner. The former should be an expert in the field of your project, the latter not necessarily. His or her job is to reel you in each time you’re about to abandon the whole thing. And believe me, sooner or later you will find yourself in a situation where you want to throw the thing out of the window. There is very little certainty you’ve done your best underway, though you may very well have. So it is mandatory to have personal support because self-motivation doesn’t always work. Never underestimate your inner saboteur. He’s very patient, just waiting for the right moment to strike. Cover your back.
Then, start breaking down the whole thing. What parts does it consist of? What are the milestones? And, something that is overlooked quite often, what small parts can you incorporate in your daily routine? In every complex task, there are exercises or other routines which, when complete, will have become your second nature. But they only will when you include them as early in the the whole process as you can.
Also, allocate specific times when you fully commit to work on this particular task. No distractions. Creating this kind of external pressure often has more long-term impact than devoting a large chunk of time every now and then. This is why it’s important to have your sparring partner, who’s to make sure you stick to your regular appointments with the task.
Regular review is also very important. Every time you reach a milestone, take a look back and check on how it’s been going so far. Keep track of all your moves, where you were wrong and how you came back on course again. Don’t forget to put little rewards at every milestone, because you can’t be certain there will be rewards from others. Quite the contrary. Sometimes, the better you do, the more external resistance you will find.
Brace yourself. Persist. Good luck.