Is the starting point in sketching important?
The starting point is important, but there isn't a single right answer.  What will work best for a given person depends on how they visualize things, and the skills they have developed.  Your result turning out &quot;not that good&quot; is likely due mostly to not yet having developed sketching skills comparable to the artists in the videos.  It takes a lot of practice to become good, and to develop a process that works well for you.  You may even find that as you develop your skill, a different starting point works best.  Experiment.
A common starting point is the environment or background in which the subject will exist (at least something crude for placement and scale of the subject).
It's useful to start the subject (either before or after roughing in the environment), by crudely sketching the outline or major parts of the subject.  This gives you a basic shape and scale to refine, and against which to develop the detail.
Some skilled artists start with an &quot;anchor feature&quot;, a dominating feature that they build around.  This works best with a lot of experience, where you've developed intuition on scale and how the rest of the subject relates to that feature.
The most important element of the &quot;starting point&quot; is that it involves starting; putting pencil to paper and moving it to create some initial structure.  It doesn't make much difference how bad those initial marks are.  They provide a basis for comparison against what you're looking at or visualizing in your mind.
It's easy to see where those initial marks are wrong or off, they provide something you can adjust.  The eraser is at least as important a tool as the pencil (not to delete everything because you aren't satisfied with it, but to make corrections and iterations to move from the starting point to your objective).  Once you get something on paper, where to go from there becomes a lot easier.