1.step -- BE ACTIVE,if you wanna win you need to be a lot active log in into game whenever you can and make sure to do all your stuff before going to bed if you dont have much time to no life you can purchase security council that can save a lot of your time and you will have much higher chanses of wining solo (kinda sad its pay to win but high KDA players ussualy always have security council bought) note that you can also play from your mobile

2.step -- HAVE GOOD ECONOMY this depends on your country but you should always build arms industry in cities you need most resources of if you have a lot of spare resources (for example components) make sure to use them dont research tehnology for something your economy is not capable of mass producing I always have maxed arms industry for all resources in my homeland cities expect fuel (fuel is useless lvl 1 arms industry for fuel should be enough fuel is only problem in early game) for your military always research and mobilize something that takes components and supply (balance it out because you always have limited number of it and cant produce all of that ♥♥♥♥ that consumes components for example) otherwise you wont be able to mass produce and have a big army always be low on resources so you always produce something with it and maximaze its production from arms industry and expanding,taking cities ect..

3.step -- HAVE A GOOD NAVY if you picked landlocked country you wont be able to win solo key of winning solo is having good navy so you can go all around word and conquer everything navy is very important because it can attack homeland cities and stop production,destroy buildings on costal cities and then prepare for your army to come if you just send your army without navy against good player it will be destroyed you always need to clear seas first and its very important
HOW TO USE NAVY AND WHAT TO BUILD? - build cruisers or destroyers with naval officer and subs,officer is important because he will boost your range so you can use hit and run strategy that basicly is you spot someone you hit him and run and dont get damaged back with this you can win every naval battle range from officer is also good because you will be able to attack more cities from distance

4.step -- HAVE GOOD DIPLOMACY this is a very interesting and harder skill in conww3 always look up and comunicate with others you can manipulate someone but dont be ♥♥♥♥♥ and never backstab always check profile of someone before attacking,if you see someone is inactive or you think that he has small army abuse that and take free territory since you are playing solo this step is pretty important and you will need to play mind games to win if you see someone strong and big you should know that war with him will be necesary in future so you should already plan on how to destroy him (look his homeland cities building and you can assume what army he has from that or use spies)

MILITARY TIPS : always attack someone, always take as much territory as you can how you do it depends on your strategy there are a lot of ways but you should always prioritize to gain as much as you can while losing as minimum as you could (my tip is to just spam strike fighters to enemy army and then your troops just come and take territory always gain info if there are some troops in city before attacking it and make sure to clean them eather with big stack of infantry or airforse before enterying never ever suicide your army and be careful of where you send it

WHAT TO RESEARCH AND WHAT TO NOT
DO:
-- research national guard and use it to conquer territory they very cheap but dont upgrade them
-- always have some strikefighters and (optional) if you are surrounded by lot of countries build helicopter gunships early game to clean
everything more easily(they have a small range so thats why I said they are only good if you have lot of enemys or countries near you)
-- always have an elite infantry stack in your game as your land army I suggest in this stack to have : Infantry officer,tank
destroyer,motorized infantry,mobile sam
-- always have some anti air in your stacks
-- As your artilery only good one is MRL(multiple rocked launcher) and you should have it it can be very useful for attacking army from far
away for example if you think enemy has anti air and your airforce cant destroy it use your MRL
-- THEATER DEFENCE SYSTEM late game make sure to have them for defence against missiles and nukes in your homeland cities
-- TO SUM UP build large navy,large airforce,and for land just have one good stack that has very good stats or more in late game
DONT:
--dont research ANY INFANTRY BESIDES MOTORIZED AND NATIONAL GUARD (special forces can be very good in late game tho)
--dont research TANKS and ARMORED FIGHTING VEHICLE they cost a lot and you wont be able to mass produce them never research them especially in early game
--dont research TOWED ARTILERY(it isnt that useless its ok in early game but its better to focus on other