Jumping oxers feels like any other jump🙂 As long as you are confident, and you ride your horse forward and straight, you will jump it. Take it slowly, and maybe start off a little lower then you usually jump. I hope this was helpful!
i personally don't feel a difference between the vertical and oxer when my horse jumps it (unless it's extremely wide). . .the largest i've done would be like a 3'3 height and a 2'6" spread, & my trainer just really wanted me to make sure i rode to the base to the jump, long ones are not helpful when you get to the bigger oxers. . .you'd be making the oxer wider.
If it helps you, this is what I do. Pretend that the back rail is an upright, ignore the front rail and the horse will figure it out. But also just remember it's just like any other jump, there actually is no difference. Horses don't know the difference either
I don't know what you mean by tips, it's the same as any other jump. As long as you are confident in the height you're jumping, give it a go! I would recommend lowering it (for example if you jump 2'3 on average, lower it to 18") I would start with it very small in width, maybe even as a crossrail, then move it to a vertical. Slowly widen it when you are comfortably jumping it. The key is confidence and taking it slow!
Hope this helped,