What I realize in hindsight was that doing the same dives over and over between C1 and C2 reached a point of diminishing returns. I probably had done about 50 C1 dives when I took C2, but they were all along the same three or four main lines. GUE's stated minimum of 25 dives between C1 and C2 is probably about right as a minimum, and doing some more beyond that is worthwhile--from what I've heard others say, around 50 seems pretty common. But if you find yourself doing the same dives over and over and feel like it's getting repetitious, like handling the reel is no longer a big deal, and you have played around with various routes to run the line into the main line, then maybe you're ready for the next course. Sure, there are still more things you can do if you're determined to really take your time and are a bit of a masochist. For instance, someone told me a mentor had them run the reel hundreds of feet into the cave, in high flow (Ginnie), before tying into the main line (at the Lips, if you know Ginnie), just to push their reel skills. Impressive, but I'm not sure that would have helped me that much in preparing for C2.