As with most professions, freelance writing will not work out for you if you have to
drag and force yourself to accomplish work. There's just no way around it. Although I do believe that exposure to the field will help because it will enable you to get more used to turning in papers with stricter deadlines. If you want, though, to have flawless papers, then you're going to have to take your time.
I do still find that if I take up work from fields that I
know, I can turn in papers faster - and with less hassle on my end. A huge chunk of this is because I can accomplish the writing tasks without needing to worry if the information I have provided are factual.
This is also the reason why choosing a specialty in writing is vital, especially because it will enable you to focus on a
particular topic without needing to burden yourself too much. In the long-run, this will help the longevity of your career.
I suggest that in the short-term, don't exhaust and drain yourself too much. It will only strain you and cause you to be less productivity. It is also important to work on time slots that are perfect for you. I, for one, know that I can only work during nighttime. There is no way in hell that someone can make me work during mornings - unless they want me to turn in poorly curated work.
Again, knowing what works for you as a writer is key to all of this.