From my experience having just finished third year at a DO school, the purpose of third year is to get good at being a medical student, and learning what it means to be the intern, the resident, and the attending.
You should spend your third year:
1) Getting really good at doing H&P's. Focused but thorough (with differentials in mind as you are doing the physical), well-done, and fast.
2) Learning MEDICINE. (I feel like procedures were always just an added bonus if whoever you are with is willing to teach... it's not necessarily the focus of your training right now and you can always learn those in residency.)
3) Becoming skilled at giving a long, thorough presentation of a patient you just saw (~15 min.), a more focused presentation (5 min.), and a one or two liner of the most pertinent information (30 seconds) to a resident or attending.
4) Developing a sense of "what would I do?" Develop your own assessment with a differential of the most common and most dangerous and a plan (even if it's limited) and be able to defend it to your senior. Learn to rule in or out differentials and rank them in order of likelihood based on clinical presentation, imaging, labs, etc. Question why the team is making the decisions they are and what the alternatives would be. ALWAYS try to read the EKG and imaging yourself; don't get into the habit of trusting the radiologist's read.
5) Being a student: Paying attention to lectures. Preparing for shelves. Preparing for surgical cases by reviewing anatomy, indications, complications, etc. Conversing with your residents and attendings (read, ask questions, share literature)
6) Knowing your patients inside and out Learn how to interact with patients so that they trust you and don't just consider you as "just the student." Get to know them to the point that you know everything about their medical and surgical history, their social stressors, their personalities... residents/attendings will be impressed when you know your patients better than they do.
7) Learning how to become a valued and trusted member of the team. You will have to find your niche as a medical student. Sometimes that means doing scut. But everything you do, you must do it well and with a smile on your face.
These things are what will make a difference come fourth year and aways/auditions. By the end of third year you have to evolve from just being a scut-monkey "information-getter" to someone who can actually think for themselves and converse/interact appropriately with residents and attendings.👍