1. Download and install OpenTabletDriver.
https://opentabletdriver.net/ .If you already have installed your proprietary driver software of your tablet beforehand, Try to close it's process to prevent any conflict issue.
2. You can start messing around with default ratio of 1.7778 just to keep things simple. Now, most people who play with tablet consider around 60 - 80mm width size to be average tablet area. I've seen people go smaller than 50mm and are mainly aim/DT speed players with emphasize on snap aiming but let's start simple. Try and see it for yourself!
3. If you struggle reaching for jumps, decrease the area by small amount (2.5mm for example). If you overshoot and misaim jumps instead, increase the area.
4. Go to either osu stable or lazer client, and enable raw input (stable) or high precision mouse (lazer). Note that when you're playing with tablet, it's kind of strange to put any additional cursor sensitivity in-game so i recommend you to keep it's value at 1x.