Literally just turn faster. Do one-handed drills to get your turning speed up, and also to get the algs in your muscle memory. Assuming you're using your left hand for OH, use your pinky for R/R' moves and your index for U/U' moves, and mostly hold the cube with your thumb and middle finger. (Thumb-and-ring grip is probably fine too, and it lets you use index-middle double flicks for U2. I'm not an OH expert, so I can't tell you which is better.)So im going to a competiton and I want to compete in OH which im starting to practice for like the first time ever and I average around a minute.
As long as you're not reinforcing bad habits, sub-45 shouldn't take very long. Maybe a week or two?