Vaulted ceilings are popular exposed timber beam designs but also offer their own challenges. You can approach it in a number of different ways. For example, LED strips around the top of the frame before the roof slopes at a wall plate level can look amazing and offer a surprisingly large amount of illumination to the room. LED strips are readily available in soft and pure white light and you can even get other styles.
Another option is to add a pendant ceiling light as a real feature in the room. If you want to go for this approach, you need to get the hole drilled and first fix in the wiring before the roof is tiled. That makes it easy to just drop the cables through and attach them to the light fixture before attaching its fixtures to the exposed roof beams. This allows you to have a centre feature light and you can still use LED strips if you want to increase lighting levels in larger spaces.