one word: blitzkrieg
my advice is to build first jet bombers and artillery and make sure that you prepared your defenses well on the border
you should be build more enough jets to affect fast in the attack and active patrol mode,
after that move your forces (i advice to do attack with more tanks and air defense) towards the provinces and then nothing will stop you
of course more advance army more easy win to have

To be ultra aggressive in the opening days of the game you need:
- Armored Cars
- Artillery and rocket arty
- AA and maybe some infantry

Don't focus on economy for the 1st day or 2. Don't build industry.
Build just military production and push quickly into enemy territory to keep feeding your economy through conquest.

This is HIGH risk but HIGH reward if you want to take a nation out quickly.

this could work if the enemy was offline, if the enemy was online and expert then he will absorbed the attack and maybe he could be prepared for a counterattack

Scout with fighters, Armoured Cars and Forced march, Arty creep.

If you plan your attacks so that one army engages with your AC, then when the battles won you Force march the AC over to the next region to join the next battle. Slower than running two battles in parralell but you end up with greater firepower and take less damage overall. Allows your armies to mantain health and penetrate further. Taking damage and reduced Damage efficiency is a vicious cycle that slows down your armies. You need to win quickly with overmatched firepower.
Same deal with Artillary. If regions set up well your arty can support two battles.

Once you break through the lines you break off your AC's and dash ahead to grab regions. Your troops move faster when they don't have the 50% speed deduction. Save 5 minutes by toggling forced march within 5 min of region center.

The best weapons for fast action are bombers. It's also advisable to have fully mechanized stacks.

Basics - Build AND upgrade Industry/Local Industry in all your core (unstriped, also starting) provinces that produce a resource to boost that resource.
Always prefer to take fights where your army has the most power advantage over the enemy. ALWAYS.
"Your army" referring to just a single army! Your units mustn't be spread out in multiple divisions even if they were close to each other.

When fighting with Infantry, do not move into an enemy waiting army if yours isn't 2.5+ times larger. If the enemy is moving and you are as well, stop moving when within about 1/5 of Artillery range of your enemy. Then leave your army waiting, let the enemy ram into it and don't give any orders to your army during the fight.

Bombers can also be very useful. Again, numbers matter! The advantage of bombers is being able to always pick the most effective engagements. Merge them into groups of 10 and patrol over the smallest enemy armies you find. 10 tactical bombers could get rid of 30 Infantry like that in an average game.

At the later stage it is important to research higher levels of the units, BUT you must upgrade the building a unit is produced out of as you research higher levels, to avoid long production times.

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For revolts, never (!) garrison your armies in worthless provinces. Usually leaving an army in each city is enough. Far the best way to get rid of revolts though, is: attack just after daychange and take as many of the enemy provinces as possible before next daychange, the capital being the last of them. Revolts happen at daychange and capturing a capital gives +10% morale to all your provinces instantly, so all the 25% morale provinces (the standard for newly conquered provinces) will go to 35% morale before daychange. As there is no chance of revolt above 30% morale and revolts happen at daychange, this will eliminate revolt chances in all of the 25% morale provinces - except the capital itself and the provinces taken after it.

Another tip is not to build needless buildings early: more production buildings than you need is BAD in early game. Try to avoid having more than 1 per city. Don't build more production buildings than you can continuously produce out of.

Don't build any recruiting stations before day 3. If your manpower decreases by about 1/4 in 24 hours it's time to boost it by building and upgrading recruiting stations in core provinces that don't produce a resource or are cities.

Don't build any propaganda offices except in your core cities, occasionally non-core ones if you need faster production and have a lot of food and goods.

Now to the overall most successful builds:

Allies: Build tactical bombers and artillery, sell food at the market and buy the needed resources (works very well). Focus on economy early, or take advantage of faster production and make a ton of units the first two days.
Later you can add mechanized infantry, commandos and airforce. Research higher levels of your units and upgrade them, multiple levels up if possible to save resources.

Axis: Build motorized infantry and attack bombers early. Attack a player at day 2-3 (when you have 6+ mot infantry) and use the capital trick to eliminate revolts. Attack bombers will be very good for destroying tanks, as long as you keep them merged.
This leaves you with sufficient resources for industry, definitely make use of that and upgrade it to max level within 5 days. When your oil and metal production gets far ahead of your daily expenses, consider adding medium tanks as Axis have them buffed significantly.
Always remember to upgrade units to high level (but wait till your currently researched level is far ahead of the level of the unit). Axis are good at focusing on few unit types and still getting good results - for example, motorized infantry, attack bombers, SP artillery, Interceptors and submarines.

Comintern: Focus on getting new cities and outproducing your enemy, but always fight with numbers advantage - it's better to push slower so you don't get caught in a bad fight. Comintern are good in straight-up fights (with equal resources spent). A lot of artillery, infantry, heavy tanks and anti air is a good slow force. I recommendd using cruisers for the navy as they also have a buff aside of being pretty good already.
Never forget to boost your economy, however, Comintern leaves you with a lot of metal and oil so upgrading quickly shouldn't be an issue.

Pan-Asian: Build a lot of armoured cars, light tanks and artillery early game, also interceptors from day 2. Invade enemies by sending your armoured car stack forward to capture the provinces in the back and wait next to the capital for the capital trick, and the infantry with artillery behind should invade the part closer to your territory.
I recommend invading a player country first, then two AI countries (to give an extra +20% to the morale of your core and the newly conquered provinces). Pan requires the player to be very active. If you are, use intelligence and military sabotage spies to reveal information, then sneak in with fast raiding units whenever it seems safe, but avoid brainlessly rushing into enemy territory, especially if you haven't revealed all enemy armies recently.
Pan-Asian is good on large fronts, so having allies whose land you can use to attack from multiple sides can be very valuable. However, make sure it gains you a lot of advantage and doesn't just get you in less effective engagements.