Capturing and discussing ideas through sketching improves your designs. However, you need to make an effort to keep the process productive. Here are some considerations to speed up your exploration of ideas.
Being pragmatic
The perfect is the enemy of the good
Your sketches should not be intended to be presented at a museum. Sketches look unfinished because they capture evolving, unpolished ideas. You can spend time making sketches reflect your idea better--adding annotations and even highlighting some elements--but you should spend no time on purely aesthetic or style considerations.
If you are a perfectionist, you'll need to practice being comfortable with lines not being straight. You need to remember that moving fast...