What is trade? Why trade is the exchange of goods or currency for other goods or currency. Now that sentence got a little confusing, but you'll get the hang of it. To set up a trade deal first you'll need to know what type of deal it is, this can get confusing.
In a modern world "I'll trade you this, for this", In bulk amounts, Isn't the best way to go about things. And to be honest it wasn't in the ancient world either.
There are two ways you can go about business. That involve the two Sectors of your country in terms of money and economy.
Private Sector Trading
Private Sector Trading is where a business within a country does trading. Now as you are RPing the state, You don't have control over this but the state can own private businesses, and support them. So you can use this to give your economy a boost here's an example of RP where a state has supported a company that is registered within their country:
To an extent you can also Roleplay as a company within your country, Securing deals for them, and expanding them over seas can increase your revenue. Here are a few Examples:
A Rarer type of deal that can be used in Private sector trading ties in with Public sector trading. The government can sponsor a deal with another government to allow a company from one the other governments country to extract certain raw materials from their land. This only is valid if the Mineral rights to land are owned by the state, if not this becomes pointless. However this method of trading has been used several times, Most commonly by the Republic of Greater Melanesia, A state with a great abundance of raw metals. The state sponsored companies like Akamai Industries from Hawai'i-Qatar to extract raw materials. This involved a tarrif on raw materials in exchange for first access to world class deposits. This is a more complex form of trading, But can be quite profitable.
Public Sector Trading
Your nation, Naturally, produces a fair amount of raw "Natural Resources" Itself. These can be imported on a regular basis to another country, for a fixed regular price in return. Said price Depends on the desirability of an item, for instance Oil is a very desirable item, where as gravel, not so much. To see what you can trade with another nation visit the Natural Resource Database page, which outlines what countries own what resources, where these resources are imported to etc.
Naturally your people want rare, and useful goods imported too so it's a good idea to import goods from other countries. it keeps the economy going, and helps your neighbours and friends do business too.
You should take note that Trading is a flow of goods, and not a single trade. It's not my 500 barrels of Oil for your 60 diamonds. It's a flow of goods for currency, a flow of currency for goods, or a flow of goods for goods.
Another integral part of trade between nations is 3rd party processing of goods. This involves your oil being refined in another country before it is sent to your customers etc. These kind of deals can be very lucrative for both countries, making you not have to invest in it, because other countries will, and they get paid for their services.
Trade networks are Groups of states that survive by trading with eachother, forming "Trade Alliances" much like that of the EU in order to boost economies of all nations. EoEP examples of this are the CTO or the CoSES
There are several Diplomatic actions that a nation can commit to ranging from War to Union. Here are prime examples.
A Military Alliance Is exactly what it says. It is an alliance that involves military cooperation on a higher level, including declaring war on those that your ally declares war on, helping them in war, joint training exercises etc.
A Union is when more than one nation unites to create a Larger nation, This is one of the most common diplomatic relationships in the EoEP, The most famous of which being the AU, which is the largest collection of players to form one state.
A Trade Alliance is an alliance that involves Economic Cooperation, usually includes Tariff-Free Zones, Centralized Currency, etc. This may vary upon every alliance. An Example of which would be APEC (Asia-Pacific Economic Cooperation) or the CoSES (Confederation of Soverign Eurasian States).