using a pre-study or not?

My art teacher in high school  used to yell at me for being impatient and easily satisfied. She said I really had to study the objects, absorb every line, feel the passion. Sketch, sketch and re-sketch. By making studies I should have been able to dream the lines and it they would flow on the paper.  So I did, only because I had to, and the results of my actual drawing were boring, childish and lifeless, which is pretty lame if you have to draw a still life.
There were a lot of moments I even regretted taking this art classes. I experienced her way of teaching as oppressive instead of the liberation that I craved. I passed the exam with a meager grade because I was full of doubts and felt so much pressure. It also made me doubt my way of illustrating for years.

A year ago it suddenly changed and I got encouraged to pick up illustrating again and from that point on I decided to do it MY way.
I don’t like to sketch and make studies, I just like to put in on paper and see where it goes. And there is always that moment when I’m drawing, I want to give up, but I’ll go on anyway.

I like to know how you do this. Do you make a sketch or a study? Do you just jump in to it and see where it goes?

Greetz ~ Anvae