I'm nothing close to pro or semi-pro, but here's a few tips :
1. Watch replays of games you lost. Try to find the problem with your play. Why did they enemy have more units at the same time? Why did I lose that engagement? Was that unit worth using in that number? Was my tech too late? etc... once you know the problem, answers come easy.
2. Watch pro / semi-pros stream on Twitch. Propagandacast / GeneralsGentlemen casts are good options as well.
3. As for OKW tips...
a) Try volk-kubel-volk-volk on open maps, or don't get kubel altogether on enclosed maps like kholodny ferma. Langreskaya is a good choice to use kubels.
b) Dont get more than 4 volks.
c) Learn when to give up certain portion of the map if your units are not strong enough to tackle their front. You can always cap elsewhere if they have an area locked down. Locking down requires units watching it. Units watching an area cannot go around capping.
d) Minimize damage taken by sturmpioneers. OKW players have a tendancy to overestimate their strength - they are only strong if they can close without being focused. Once focused, they quickly drop, and losing a model means severe dps loss.
e) The meta used to be T1->T3 using fortification/lufewaffe for MGs, but these days many players are using T2->T1 to survive greyhounds and M20s.
The tech order really depends on enemy play and the map - a fail-safe, easy option is going T1 -> T3 and get obers and luchs(if too late, panther) for infantry domination.
f) This is probably obvious but never lose a unit. Losing sturmpio, Puma or Panther usually spells disaster. OKW cannot afford to lose anything that costs fuel OR sturmpio. DId I say that enough? Never lose sturmpio...
g) Truck placement is mostly fixed these days. Top rankers have already figured out the most efficient/effective places for trucks - especially Flak SWS and medic SWS. Key point is to have them out of LOS while covering key flanks or holding a critical spot. This is best learned from ranker streams.
These are my thoughts in OKW 1v1. I'm not that great a player, but I can share things I've learned from watching streams