The main thing to grasp for dual playthroughs is focusing on story first then optimization later. Take your time going through main quests naturally, mark down your choices for romance and major decisions cause youll want different outcomes next time. Before jumping into ng plus make sure to craft some witcher gear sets since they scale up nicely, and stock up on those rare materials and mutagens they're super valuable.

For the second run you'll be way stronger so thats when you can really experiment. Try those different story paths you skipped, tackle high level contracts early in skellige, and maybe test out some wild combat builds since you'll have tons of skill points. Just remember some side quests like frying pan and precious cargo get locked out after certain points, so keep an eye out for those if you're hunting achievements.

Good to know: pacing is important, make sure you're following the main quest order properly like finishing lilac and gooseberries before hitting up the imperial audience. Having all that carried over gear and abilities lets you focus more on exploring those branching stories you missed first time around, which is honestly the best part of doing two playthroughs.