I’ve been working on a lot of the Intermediate tricks from the tab above, and I seem to be having trouble keeping the string centered on the yoyo. I mainly have issues on split mount tricks like the Mach 5 and split the atom. I can’t get the yoyo to stay vertical long enough to complete the tricks. Are there any tips to keeping the string centered? Or should I just invest in a concave bearing? If so, which one would you recommend? Thanks
Just work on your throw. The yoyo is tilting because of your throw, not because the string isn’t centered.
Not really sure if that is it. I always make sure the yoyo is straight when I first throw it. If it isn’t, I bind it back up into my hand. I always make sure the throw is straight before I start one of the tricks.
It’s easy to make a yoyo tilt DURING the tricks. Your technique will get better as you practice. When you do a split bottom mount, you’re already in a position to tilt the yoyo like crazy if the two hands aren’t in perfect alignment.
Work on getting into the mount quickly and then you’ll inevitably start developing muscle memory for where the hands need to be in relation to one another to keep everything from tilting.
Trapeze and virtually all other mounts are the same way. It’s about the alignment of the string that the yoyo is mounted on. The string needs to run perfectly parallel to the walls/rims of the yoyo to minimize tilting. Unless of course you’re already tilting, then you intentionally put them out of alignment to correct the tilt. 
Greg is 100% right, but a harder throw/ faster spin can help to, gyroscopes work better the faster they spin, so it might be a little of both. I know my Mach 5 moves all over the place but as long as you keep your hands moving around the yoyo it shouldn’t get a chance to skew too far in any 1 direction