Returning to the whole picture from time to time
When we design a course from scratch, we have the whole picture. We identify ourselves with the design, and the course thrives on this identification. On the other hand, when we use a syllabus that is already laid out for us, or even when we reuse our own design next time, it may set us in driven mode rather than driver mode, of following a given path without much control. We may notice several glitches and bumps as we teach or prepare to teach, like:
- Major flaws in the design
- Topics that we wanted to do better than the last time
- Topics for which we wanted to try different approaches
- Required adjustments to relative emphasis of various topics
- Need to change or introduce new exercises
- Need to incorporate new things in the field
- Need to incorporate our improved or alternative insights
- Obsolete things (especially in technology) to be reduced or removed
- Need to realign the course in the larger view of the entire programme that the course is a part of
But it may be too late to do anything about these when we notice them, since we also need to prepare for the actual lectures. Thus we may start loosing our identification with the design.
A few reviews, done consistently, can help us keep the design up to date, and maintain our identification with the design: First review is that of the entire plan, well before the course begins. And then we need periodic reviews while the course goes on, such as biweekly or monthly, of the remaining plan of the design. These reviews help us notice such things in time, and gives us chances to incorporate such things in a timely fashion. We can reestablish our identification with the design, keeping life the course.
Such a review may however be overwhelming, because we may notice a lot of stuff that needs to be done. A step by step approach can help us here:
- Keep the review just a review. Make no changes at the review time. Just note down whatever occurs to you while going through the design.
- Later on separate the notes into distinct, possibly related, desired outcomes.
- Work on each of them one by one.
When we know we are teaching according to our best plan, teaching is an amazing experience!
Abhay Parvate 
I am not sure how much liberty do you have in having your own syllabus keeping the aims same. As far as the tools/instruments go, we can do whatever we like with a course. I remember I had entirely different assessment than the one before and it did not include written exam and it was very successful. Any way you can design the task but you have no control over the activity that a student does. So why not be flexible? you said it correctly, teach according to your own plans. I agree that teaching is an amazing experience.
You are right in that usually the aims of a course are given to us, and we cannot change them, not at least so much that they start contradicting the larger picture. And for well established subjects, given the aims, there are standard expectations as to what topics should be covered. That in a general sense then becomes the part of the aims.
But one always has the freedom to organize and modify the material and/or the presentation for various reasons as in the bullet list above. And unless this freedom is exercised, the course will loose its charm. So again as you said: it’s best to use our experience to adapt flexibly.