Deception is the key

Assuming you want to go solo all the way (rather than joining an alliance early on for protection and leaving later) you'd better make agreements with SK and at least 2 of China, Russia and Japan as they always tend to destroy NK early on. Just tell them not to attack and you wish to build your cities before you join and help them Diplomacy works.

You need to dig in and make Army Bases in all cities followed by infantry in all cities. Then Arms Industry 1 in your supplies city. Supplies are essential early on - you can't build infantry, research or build industries without them. They are the key. Research Infantry and Recon vehicle. Many here don't like recons but research is 30mins and they provide you with some armour to punch through in the early stages. And you can see your enemy ahead and change tactics if necessary.

It also all depends on the active users, how good they are and this is totally random

You need territory in this game so SK should be your first target after you've made another round of infantry units. Check his cities for army bases. If he hasn't built them then he hasn't got more infantry and you can stack up and overwhelm him. If he is active and building then switch your focus on Vladivostock (Russia). Russia is often busy in other theatres and transport to the east takes time so you can overwhelm him there. But that all depends on how active/experienced he is...

I would do it the other way around. If SK is active and you don't want to ally with him, attack him first - and quickly. Nearby active players who you're not going to ally with need to be destroyed as fast as possible so that they don't have time to build up their strength. Also, if you move on Russia while you have an active SK player on your other border, you're leaving yourself exposed to a likely attack. If SK is not active, you can afford to commit units to attacking elsewhere without worrying about them until afterwards.

I would want to see this game.