I generally don't play 1v1 but here's what I did in my "practise 1v1" games and it mostly worked.
Try to advance keeping your units close. Go for the near fuel, one Volks and one Sturm should go side by side so if one encounters the enemy, the other can react and run to help. One Kubel is good but keep it safe, don't advance too much and keep it always behind your infantry. Then, another Volks and if all is good, I bring on a Rocket launcher. Hide the Pupchen until you see the enemy armoured car or he may be scared and not build one.
I generally go Luftwaffe, but Panzerfusilier giving doctrine is also ok for me. When the MG34 and doctrinal infantry come to help, if you haven't been wasted for now, it's fine. The thing is, do not rush your truck and try to gain ground. You need to fight and keep your men alive. Even setting up the truck close to your base is ok if you thing you'll risk too much by getting far. Keep your troops together, maybe in 2 groups close to each other. When one encounters the enemy, flank with the other. Do not run to the far sides of map to gain points. Defeating the enemy forces and not having your men killed is more important than gaining ground.
The first building is great. It gives you the artillery gun(a perfect weapon) and Jagpanzer (the middle AT for OKW) Now, all is great, you have everything you need in mid game; infantry (Volks + doctrinal), artillery gun and Jagpanzer. The main problem here is enemy Sniper, for which I have no easy answer. Just try to catch it alone with Kubel or a flanking infantry unit and run away from it if it seem to kill too much. Sniper means trouble for OKW, just try to resist, giving ground is ok if you can protect your troops.
I generally skip Mechanized building and go for the Shwere. If Sniper's a pain in the ass a light tank can come but watch out for AT guns. Silence AT guns and Snipers with your artillery gun if you can. When the Panther comes, it's generally GG.
Hope I could give some help
Good luck, OKW is real fun...