Great purge is going to happen and you have to lost some great Field martial like Tukhachevsky but try to keep the lost to the minimum. Political Paranoia is a problem if you are going non historical pass but not for this game play. Raising the political paranoia and lowering it is well balanced in the focus tree. I would suggest to rush down the The Bloc of Rights and Trotskyites as fast as you can, while concentrating mostly on the focuses coming down from The Path of Marxism Leninism. In other words, ignore the industry and army focuses, you will get plenty of time for them.
Here are some recommended focus sequences:

1. The Path of Marxism Leninism (pp+25)
   
2. Addressing Internal Affairs (pp+50)
   
3. The New Soviet Woman (pp+70)
   
4. The Centre
   
5. Expand the Agitprop (pp+25)
   
6. The Zinovyevite Terrorist Center (pp+25)

Other focuses are not as vital, just try to keep political paranoia as low as possible while you are doing other things, and it should be fairly easy.
During the early war against Romania and other countries (more detailed in next section), rush down the focus War Heroes. You need to start train your Field Martial.
For the industrial focus tree, I would suggest National Specialists and Reorganize the PC of Heavy Industry. If you time the thing right, you are able to get most of the third five year plan down.

Let's take a look at normal USSR gameplay. We can find out that the southern front of the USSR is way easier to break through and vulnerable than the northern front because Axis can attack from multiple directions (Romania, Germany, Hungry, etc.) And also, remember that one of the most OP focuses of Germany, Integrate War Economies will bring Axis tons of military factories. Thus, my goal is to eliminate Balkan countries and eastern Europe without fighting the Allies before 1940.
At the start of the game, we need to bank up as much political power as possible because we will use them to justify the war goal.
We are going to justify Turkey and Yugoslavia. The reason is simple. We want military and civilian factories from them. And we also don't want to deal with south flank of Axis and numerous Romanian troops in the inevitable war with Germany. Romania guarantee Turkey. And Yugoslavia is guaranteed by Czechoslovakia and Romania (the guarantee from France will be revoked through the France focus tree, and if you are playing on historical, you can always time this right by the following steps.)
Once you get around 130 pp at any time, you are going down the above sequence, justify on Turkey, justify Yugoslavia, cancel the justification on Turkey, justify on Turkey again. Therefore, it is possible to declare war against Romania and Turkey within 60 days of difference. By the time the justification finishes, the french guarantee should be revoked, and the Balkans and Eastern Europe are in no match for Soviet Red Army.
Pause the game once both justifications are finished and declare war on them simultaneously. Use mountaineer force to break through Turkey's eastern front and land some troops near Sinop and Samsun to distract the Turkish force. The priority are Romania->Yugoslavia->Turkey->Czechoslovakia.
The only difficulty should be against Czechoslovakia, and others are pretty easy. An easier way to defeat Czechoslovakia is to create a pocket in Northern Transylvania, wait for the AI troops to swarm in the pocket, and use the tanks to cut their back. There will be no defense in Czechoslovakia as all the troops are cut off.
After you annex them all and get eastern Poland and Baltic states, the battlefield is away from the core territory of the USSR. Start justification on Hungry right after France capitulates, so you can eliminate Hungry before they join the Axis, and they are not likely to get any guarantee from Allies. I would not suggest fighting Bulgaria because it is easy to crush, and it is pretty hard to time the justification without getting into a war with Allies or Axis.
All left for you is micro-managing and creating encirclement with shock troops and tank divisions. You will likely have more starting troops and factory counts than Germany, and you can win/ hold the war reasonably easily from this setup.

Focus on Armor, fighter and Tactical bombers, and focus on producing AA and fighters. You need to win the air battle against Germany, and you will have the military factory to do so.
The template I am using is 10/0 pure infantry with support, like:
Then slowly adding more artillery to a 10/1 and eventually 10/2, like:
They are just build to hold the line, and Tanks are the spear for you to cut through enemy line and create encirclement. This is a standard 40 width tank division I am using.I just use 8 of them so that it won't eat up so many supplies.

For the doctrine, go right branch of mass assault, we are soviet and we have MEN!

You can try to take out Poland instead of Turkey in the early game, and I think it will work as fine, but I love Black Sea, so this is the strategy I use.
Give Germans Sudetenland, build forts and supply hubs in the region you are still holding, great encirclement always start from this region, and let the Germans pay with blood.
Good luck in the game!

Around 120 German divisions here, hope Papa Stalin is proud of me.