As SL and Commander, always stay strategic. Remind squads/squadmates to follow orders, communicate regularly, give your forces support or die being not credit to team in any way.
Bombers, if a ground force is requesting you to bomb some place, bomb it. For Stukas, don't use wind siren behind enemy territory especially when you're not in a dive ready to let hell break loose.
Fighters, if recon or bomber needs escort due to heavy enemy fighters or some infantry are getting raped by enemy air forces, go over there. Keep an eye for anything you can destroy, and don't waste explosive ammo on light aircraft unless its an emergency (Say, somehow a stuka's gunner exists and is giving you hell for firing or a recon is spotting you and ack acks have been fed your location.)
Recon is just a humanly oiloted UAV that can request artillery barrages. Doesn't make it any less important, as it can give important information on the enemy's position. Fly high, and medium if you have a forward artillery observer in your back seat so he can see something.
Tanks, you act as both anti tank and as a mobile infantry annihalater. Grants, take advantage of your duel heavy cannons and bring a gunner and gunner/driver. Support infantry in offensives, and they will guard you from AT infantry, and hopefully disable mines.
Scouts can be the deadliest infantry out there. They can call artillery, they can report enemy positions viewable on the minimap, they can deploy anti personnel mines, and have smoke grenades to cover a getaway after their own position is spotted. I suggest when you call arty though, you ask for whether you want smoke or HE.
As a last minute comment for transports, Ju-52 oughtta fly high as dang possible as should recon and drop over tactically helpful dropzones, which vary depending on the state of battle. Land, you should always keep moderately loaded with at least 3 or more troops and have yer MG duck often enough to avoid fire and still lay down hell for the enemy.