With the tasking you need to make sure that the task is bringing unconscious behaviors conscious for the client. You want to have the client do a task that causes the client to show they have investment and or are serous about solving their problem. You want to make sure that the task has them follow your instructions and make sure they are willing to play 100%.
There are a number of ways of discovering the right task for the client. One of the easiest ways is to ask the client "what is it your not doing that you should be doing"? This is a great way to uncover the clients desires to do it or more importantly their desires not to do what they should be doing. Then taking the answer that the client gives you and then design a task or ordeal for the client they they have to do constantly, This has them and reminds themselves that they are doing what they are not meant to do instead of what they should be doing.
For example a client is struggling to finish a project that they have started. You ask them what are you not doing that you should be doing? The client answers, finishing the project, putting time into completing the project, scheduling my time to work ion the project. So the task is every time the client is doing something that is not working on the project that they write it down and email it to you each day. You get a email stating that today instead of working on the project they were cleaning up the house, doing the washing, surfing the net.
The task will bring the unconscious behavior conscious, then by documenting it and sending it to you they are being held accountable for wasting their time.
Remember the task is not to embarrass the client, you want to empower the client by them learning about their own behavior.
Post session you could ask the client what is it that they need to do to achieve their goal, you could have them break it down into daily goals or weekly goals. Then by having the client document that they will be doing it by the date they said. You then make sure they complete it, you hold them accountable to complete the task to move them towards their goal. This is the taking action part of the three things we mentioned at the beginning of the post.
So have the client focus on what they want, be at cause take responsibility for their actions and then have them take action.
Tasking is a very effectively way of putting the responsibility of getting a result squarely onto the client. If you give the client a task and they do not do it then they can not really come back to you and say this "did not work". That being said you need to design a task that will presuppose success of the clients goals, your task should course the client to have success.
One last point on the fundamentalists of how to do tasking, you need to make sure that the client agrees to do the tasking. In some cases you may get agreement before you give the client the task. This can be taken the wrong way so make sure you tell them that the task is legal an ethical if they question.