There is no wrong or right way to trade, there are only ways that earn money faster and ways that are less boring than regular grinding. In this article i will try and cover basic principles of trading and things you must take under consideration. Each station has 2 columns describing it's consumption and production.
Each commodity has demand (consumption) and supply (production) columns where we can see textual and numerical representation of two main values – how big is consumption/production for each commodity in this station and how many units are available right now in station's cargo hold.
Textual values are NONE, LOW, MED, HIGH. Those represent the actual station's consumption or production.
Demand: station needs this commodity at HIGH/MED/LOW level and over period of time the amount available will drop (consumed by station) even if no new trades are done thus rising the price.
Supply: station is producing that commodity at HIGH/MED/LOW level and over time the available amount will increase unless traders can buy more than station can produce in given period of time.
Now let's look at that in context with buying and selling.
Buying: anything that station is producing (Supply greater than NONE) is good for buying. For best profit you must only look at MED/HIGH supply and where numerical value is big, because the more units of commodity are just sitting in station's cargo hold without consumption (demand) the lower price will be.
Selling: anything that station is consuming (Demand greater than NONE) is good for selling. But for best profit you must only look at MED/HIGH demand and where numerical value is close to zero, because if station needs something but has very low or even zero amount available the price will be very high. Biggest price will be when demand is high and there are 0 units available.
This is good indication to see how current price differs from galaxy average and to calculate approximate earnings. You can always check it but when you see high demand with close to 0 units available you will see the price is much higher than galaxy average. Same goes for high supply and many thousands units available – price will be really low.
What does that mean? That means if the DEMAND is NONE Station do not need that commodity even if you bought it very cheap and will not pay even galaxy average price for it if it will pay at all, but most likely you will able to sell it at a small loss. So just buying very cheap will not guarantee that you will find a place where this can be sold. This is not an arcade market game but the game where actual demand plays a huge role in commodity consumption and supply is actual number that will be produced over given period of time and added to station's commodity market.
NONE in SUPPLY column means there is no production so there is nothing to buy.
Simple trade runs – usually those are between 2 safe systems and involves a trade between only 2 stations, no matter how many hyperjumps away from each other. There are many stations that can have such 2 way trade, usually one way nets you much more than other and best money comed from gold, but gold comes in pair with traveling through anarchy systems (usually) and it's pricey – one gold unit will cost you around 8400cr (it can be sold with 1500 cr profit per unit), so it requres some serious investment and is very risky as you can lose everything in a blink of an eye.
Basic trade runs involve iBootis (Chango Dock) and Aulin (Aulin Enterpraise), Fish to Aulin and Agr-Medicines (or if you can afford then Terrain Enrichment) back.
Coffee from Eranin (Azeban city) to Aulin (Aulin Entreprise) and Agr-Medicines (or if you can afford then Terrain Enrichment) back.
Also a safe system that any ship can reach is trading between Ovid and Chi Hercules. Fish and marine supplies is the most profitable between those 2 systems.
Ithaca to LHS417, it's a 15 min odd round trip selling one way make about 160k a run with a Lakon 6. Need just over 1 million credits for 100 Paladium though.
Asellus Primus to Dahan is a decent run if you've not long started & have around 20-30k in the bank. Resonating Seperators or Advanced Catalysers from Asellus –> Dahan. Then Tantalum from Dahan –> Asellus.
Circle trade runs – these are more complex trade runs and involves at least 3 stations but are much more profitable because between 3 stations you can find what station 1 produces and station 2 consumes, station 2 produces and station 3 consumes and station 3 produces that station 1 consumes. So while in simple trade run you will have big income one way and much lower back then 3 way trade will net you more on average and will not be so repetitive as visiting just 2 stations all over again.
Do not forget bulletin board – when you are low on cash or just want to trade with style and explore check bulletin board for missions before you buy any cargo, it may net you some extra thousands now. When reputation system is introduced the missions will evolve and you can have really good income just by doing them, but for now they are just a nice extra that adds some exploration. Please do note that on bulletin board when you see mission details you will see required jump range and it's already with included mission cargo mass, but if you are planning to fill your cargo bay then make sure the numbers you see are not too close or you will not be able to make a jump and will have to return to station and sell excess cargo.
If you know where you are going (i.e., have taken cargo run mission) you can see in galaxy map under View>>Trade>>Show trade routes what commodities you can bring along and sell with profit.