News flash, this is actually called the Double Obstacle Course. Why? Because you do it twice in a row. I was HORRIBLE at the obstacle course at OCS. I couldn't climb a rope to save my life. I went to all the remedials at OCS, even when it was snowing, and I became decent. I remember being so happy reaching to top of the rope at the OCS endurance course, because I knew then I would pass the endurance course.
At TBS, practicing the obstacle course in my free time helped me IMMENSELY. I think you have to have the instructor demo before you can practice it on your own. When you can, I highly suggest you practice on your own. Make it fun, bring music and friends. It really helped. Some obstacle lanes have slight differences, and it helped to be familiar with them. It also helped with my muscle memory, flexibility, and endurance. I paced myself very well. I didn't get the fastest time, but I was always solid, never fumbled. Better to be methodical and get through, than rush and fumble over obstacles more times than you need to. I jogged, not ran, between the sets. This helped me recover with enough energy to do the second time faster.
Practice the rope as much as you can. There's one outside the barracks. The things I was horrible at at OCS, I made sure to fix at TBS. I practiced the rope a ton at TBS and never struggled with it during the obstacle course and endurance course. At OCS, I ordered Bates Lites boots, and was mistakenly sent Bates heavy duty. This was a wonderful mistake, as the Heavy Duties were awesome for the rope, whereas other people struggled with the Bates Lites. Since I went to TBS in the summer, I got those sweet Danner Reckonings. They were also good for the rope. I loved them for the CFT, O-Course, and E-Course. I used them for all the field events and hikes. I had no problem with them but you feel the ground more when you hike compared to heavier boots. My SPI said he hated the Reckonings for the field and hikes. For me they were fine, but I definitely recommend them for O-Course, E-Course, and ABSOLUTELY the CFT.
The biggest take-away: I was really bad at the O-Course and out of all the events, practicing this on my free time helped me the most.