It will be obvious that nations have different strategies you have to use if you are somewhat familiar with the game and nations. We will start with basic tips that you can consider with any nation, with exceptions of course, and build up a general knowledge of economic improvements and advanced information you will need for a better gameplay. This guide is intended to improve your gameplay or at least give you a sense of knowledge.

Using Your Explorer & The Start of the Game

To Start with, Your EXPLORER will be of great use especially in the early game.

• Explore the environment, assess the resource locations.
  
• Get the easy treasures you can get along the way. This will be a good start.

Note that while treasures are indeed a great advantage for your nation especially in early stages of a game, getting in risky situations that will cause your explorer to take lots of damage is unnecessary and will even put you behind. If your explorer gets downed by treasure guardians, you will either have to pay a ransom of 100 gold to mother nature (which can be done from your town hall) or to go and rescue him with a group of militia or villagers.

Until Your first Age Up

Till Age II:
Focus mainly on food and wood. Might differ from nation to nation. Mostly true for every tactic.
While aging up is important, aging up as fast as possible might be a bad idea. Would recommend improving your resource gathering by getting the improvements from the Marketplace. And having 10+ villagers before aging up.

Important Notes BEFORE aging up to II:

• Build Order: A house, A marketplace. is essential.
  
• Use your deck wisely, get a villager card or the Economic Theory Card.
  Economic Theory Card will give +10% boost for all the gatherings. Highly recommended at start.

Now you have achieved everything you want in the first age, got a house and a marketplace, improved your economy and aged up to Colonial Age! Things are going great, now what? Start getting more villagers to start with, and depending on the map you need to decide when you want to go farming from hunting. It all depends on the resources available on the map, it's best to keep hunting at age 2 and start mining and focusing more on coin aswell.

Yes, you can build farms, livestock pens, and some buildings with attached berry bushes, but one of the quickest ways to get food is to follow a herd. Hunting in Age II is highly recommended.

Quick Tip For Age II: Never stop exploring.
A map explored means you know where key resources are located. It means you know where your enemy is located, and it means you know what your enemy is up to. Blindly creating military units will sometimes work out alright, but if you know proper counter units, you'll always be on the lookout for what the enemy is up to.

When your economy is sustainable enough you can advance and age up to III.
If you have problems with economy, check what is bottlenecking your economy and focus on that area. The problem might be due to: idle villagers or an unbalance of economic priorities. Beware of those mistakes.

Your Town Center should never stop producing Settlers.
Your Villagers should never be idle.

Get more Town Centers. This will mean faster villager production and more place settlers can retreat if you ever get attacked.
Get Estates and Mills, Fully upgrade your Estates and Mills. Keep everything fully staffed, with 10 workers working on everything.

Have at least 50 Settlers: Preferred is 20 on food, 20 on coin, and 10 on wood. Depends though.
Fortress Age is the best age to start creating a full-fledge army!

Everything depends on your strategy!

If you still have not been attacked yet, your enemy is probably going to boom. This means they are not a rusher and planning on economy just like you! Set up a few Outposts, and upgrade them but also get more military buildings up if you haven't already. Improve military.

When training units, try to train only those that cost food and coin; wood should be reserved only for your buildings, but sometimes it's unavoidable. If they cost wood, you might want to buy the wood through your Market.

Recommended to focus on gold and food.

Imperial Age is the best age. It is the last age, and now you can maximize your destruction force with imperial improvements.

Build up your force, and try to kill them. If you're against a boomer, they will attack soon, so prepare for that. If your defenses are strong and you see the boom happening, get your troops around theirs, and send them straight into the enemy's home camp. Your defenses should hopefully at least delay them long enough that you can take their economy away. Remember that to win, you need to destroy every building (walls excluded). If it looks like they'll get you before you get them, send your army back and try to stop their army with yours.

Focus on the enemies economy. Try to kill their undefended villagers if there are any.
Back home, keep producing units as yours are killed. Don't send them into battle directly.
Remember to have fun!

Well you can definitely play the game using a mouse only, but this will only slow you down.
Hotkeys are customizable. Check it from your settings.

These hotkeys directly focus on a specific building which speeds up your game.

Generic Hotkeys:
key space - center on selection
key ALT - display detail on selcted unit
key DELETE - delete selected unit/building
key Pause - pause game (click menu - pauses game w/o alert box)
key h - toggle Home City View
key F2 - display improvements
key F3 - display objectives
key F4 - display player score
key F5 - display chat menu
key F6 - display tribute menu
key F7 - display player summary
key F8 - quick save
key F9 - quick load
key F10 - display in-game menu
key F11 - display game time

Your Explorer needs to look for trade routes, so he can set up Trading Posts. Upgrade those as you can, and trickle in whatever resource you need the most. After Age III, Only XP is recommended.

Actually the best way to gain early XP.