The way to create with freedom and seeming abandon in a sketch is to do ENOUGH of them. That is why in life classes they start out with 5-second poses, then 10-second poses. You have to set aside mental gyrations, which are very slow, and rely on iNSTANT FEELING impressions. You have to NOT CARE about RESULTS; care only about GETTING DOWN the IMMEDIATE ESSENCE of the thing IN SHORTHAND.
SAVE THE ABOVE PARAGRAPH AND ENGRAVE IT IN YOUR BRAIN. THAT IS WHY MANY CHILDREN'S PAINTINGS ARE SO WONDERFUL. THEY PAINT DIRECTLY FROM THEIR FEELINGS. NO BALONEY-CRAP MENTAL TRIVIA.