I think like everyone says a partner who can rotate the strike (especially helpful as im a lefty) . Ive just started opening so ive batted with the same guy a lot, we rotate and have a good understanding of what bowlers we like to faceand the areas we can each score more freely, for instance I am stronger of the back foot whereas he will drive and be more front foot dominant - sometimes batting a foot plus out of the crease. This helps me because the bowlers lengths are very different. Weve put on 60* ,124, 98 86 and 79 and a poor 13. We have good fun while we bat,.