0. BIG NUMBER > SMALL NUMBER
- If you think you can win a combat, add more units anyway. Early-war Germans fight harder than their CV shows, so you need the insurance. You do not really win combats by shooting the Germans, more by having enough CV left standing after the Germans are done shooting (except against a regiment). And if you win, each unit has a win recorded, making it easier to get Guards.
- If you can have more bombers attack a forward panzer division, attack it with more. AA currently is not very good, so it will shoot, draining the unit's ammo while dealing low losses to your planes (you would lose them in air combat as soon as the Luftwaffe moves in, so seize the moment). You will slow it down and deal good damage. Motorized divisions are worse targets, but still good enough.
- If you have several HQs with artillery nearby, take at least one unit from each HQ into the attack. Lots of guns are way better than a -whatever% CV penalty your units from other HQs will get. As a Soviet general reportedly said, "With 200 guns per a kilometer of frontage, there should be no reports about the enemy". Nevertheless, strive to have the majority of your attacking CV come from a single HQ or two corps from the same army.
1. Leningrad is the most important decision
Out of all three major directions, Leningrad gives you the least amount of time to respond to German efforts: the border is close, there are ports and partially intact railways (position trash units on the double rail if you can afford to make sure it will be broken) to supply the invaders, and the terrain is good for the defense - each lost hex matters way more than a plains hex south of the Dnepr. By turn 2, you should have an idea regarding the number of mobile units the Germans sent north (even if you do not see them, they likely generate combat reports killing whatever is in front of them). If that number is substantially higher or lower than what is in that sector at the start of the scenario (open a new campaign as the Germans to check), adjust accordingly. The distribution of forces to the other directions will follow from whatever is left.
Let us look at a screenshot from one of my games at the end of Soviet turn 5. It is not an example of perfect gameplay, that game is quite old, but just an illustration.

- early-north.png (2.53 MiB) Viewed 62 times
a) The red circles: or Fortification Zones and you
Early on, your units are often retreating, using most of their movement points, which limits their ability to dig in. Combined with a not very large amount of digging support units (at some point, you get a lot, but it is later), you cannot guarantee even lv1 forts for when the Germans come knocking. Build FZ units from the top menu in certain easy to defend and important places (like the Luga line or near Staraya Russa, the forts near Leningrad are a mistake, if you get cut off on land, it will be GG for the city no matter the forts behind the Neva). These FZ units allow other units sitting on them to dig lv3 forts even while not in contact with an enemy hex, and lv4 forts in cities/urban/ports. If you refit them to a non-depleted status (100% is unnecessary), they can begin digging themselves - attach up to three biggest construction units to them, but be wary - if a FZ loses a combat, it surrenders along with all of the SUs it has.
b) The orange rectangle: defense in depth
You cannot face the Germans head-on, yet. So in places where you have a lot of units, it can be helpful to put them in several hexes in a row, instead of a triple stack with nothing behind. Even if a unit gets wrecked, it generates combat delay in its hex. Multiple battles waste more enemy CPP, ammo and so on. And the Germans would have wrecked that triple stack, anyway. Also, this formation is the least vulnerable to pocketing. However, you are guaranteed to take at least some quite one-sided losses, but it is what it is. You need time to build your own CPP to make counterattacks and trading space for time is not a great strategy in the north.
c) The yellow circle: strategic rail transport
You begin the game with randomized XP and morale on most of your units, but units in the south have a big bonus when randomizing them. These units are key to making early counterattacks. Try to keep them safe, and the south is not the place for that, with a high potential for pockets. The north, however, is. The center is fine, too, but units in the center get a smaller XP/morale boost themselves. Please ignore that the only thing coming by rail is an air HQ, that game is from a long time ago. Due to war with Finland, your units in the Northern TB will get extra XP (but not morale) until fighting dies down in late 41. Consider bringing them on-map in exchange for some trash that is too vulnerable to stay on-map.
(To be continued, probably tomorrow)