Short distance trade with handicrafts/cooking/sewing/casting for beginner profits (exp/fame not first priority)
1. Very good trade route is Antwerp-Den Helder.
You need at least level 3 cooking and level 3 handicrafts and level 1 sewing.
Let's say we start at Helder, buy all chicken - pluck feathers (sewing1, Fabric Secrets - Hardwares book, bought in Amsterdam for 5000D), buy all sheep - make lamb (cooking3, Livestock secrets - Sheep book, 8000D Amsterdam), sell lamb to market keeper (profit of 40-60k in couple of minutes). Even better if you have cooking level 5 and can make sausages (level 5 recipe from the sheep book). Then make sausages and sell to market keeper - even better profit. After doing that sail to Antwerp, sell feathers (or you can sell feathers in Calais nearby for better exp/fame), buy all wheat and pork (if you have level 5 cooking - then buy pork).
Make Akvavit from wheat ( handicrafts 3, book Brewery Secrets from Hamburg for 10000D) and sausages from pork (cooking 5, book Livestock secrets - Pigs, 8000D from Porto). Sail back to Helder and sell everything. Repeat :) It's quite good early money, can make several 100 000's per hour this way. But it gets boring quickly.
2. Bergen - Oslo if you have Historical Crafts Guide book.
Bergen has Rye and Lumber, while Oslo - Wool and Lumber.
Go to Bergen, buy Rye and Lumber, make Vodka (handicrafts 3, brewery secrets book) or Whiskey (handicrafts 4, same book), and make Wooden figures from Lumber (handicrafts 3, Historical Crafts Guide book, 400000D investment in Cairo). Now sail to Oslo, sell everything there (can make some 80-150k profit easily), buy Lumber and Wool in Oslo (Lumber->Wooden figures). Make woolen cloth (sewing 3, book Fabric secrets - Cloth, 10000D Antwerp/Helder) or knitted cloth (sewing 4, same book), even better flannel (sewing7, Fabric Secrets - Fine Cloth, 240000D invest + 100000D price) or tweed (sewing8, same as flannel).
Mid distance trading
1. Spare rudders/Spare sails.
All you need is Casting level 2 (book Shipwright Basics, 10000D Antwerp) and Sewing 2 (Shipwright Basics, 10000D Antwerp).
Sail to Amsterdam, make 400 spare sails(can take up to 5-6 trips to Amsterdam, can sail to Helder, make feathers, lamb, sausages etc for quick profits too as mentioned earlier) - 200 in inventory and 200 in store. Then sail to Oslo (more lumber on sale than Bergen), make 400 Spare rudders.
Now the problem is that in North Sea area the price for these has fallen a lot. So you'd need to sail to Lisbon to sell sails (1.5-1.6 ea, 350-400k profit, but no exp), and search for a place to sell rudders (don't really know in Europe as I always sell my rudders in Luanda when going to India or so. Can sell sails here too). So all in all you can make 700-800k profit easily, but will get no exp for it.
2. Velvet to Northern Europe. Basically buy all velvet in Genoa/Pisa (now sells it too), max price would be 4000-4500 per unit, the lower the better.
In NE you can sell it for ~5500-6000, so it is a profit of 1000-2500 per unit. Usually if I can't buy it for 4000ea I don't bother.
3. Diamonds/Gold/Ivory to Northern Europe. You can buy these in West Africa, after some investment. Problem is these sell in small amounts, 4-6 in each market with no trading skills. So metal/gem trading is a must for it to be really effective route. For example you can buy diamonds for 2.5-3.5k in Luanda and sell them for 9-10k in Northern Europe. Great profit. Cons: need West Africa permit, which is 6000-8000 fame depending on nation
4. Silver/Gold dust/Caribbean specialties/Ginger to Northern Europe. Need port permits of course.
This is the route I am experimenting right now with, as going to India takes 3 hours of sailing there and back.
Silver is attractive as you can buy it for 1.2-1.5k in Santo Domingo, and sell for around 4000 in Northern Europe. Also with precious metal trading skill you can load it up quite quickly with sailing to San Juan and back.
Another great commodity is Ginger, can buy it for 250 or so in Jamaica, sells for 2000-2500.
Also every specialty except peanuts can get you around 1000-1500 profit per item, good exp and fame. Thats cacao, tobacco, tequila, pineapples.
There is also expensive dye in Jamaica, thyrian purple or something, can get around 3000 profit per item (buy for 4000 sell for 7000).
With trade job I get around 5000-6000 exp per route, and it takes only 1.5-2 hrs at most, earning 1-2m profit (largely depends on goods transported).
Bring Northern Europe specialties to Caribs, or just Dutch Calico for max profits (sells for 1500 profit per item or so).
5. Antique art/Damask fabric/Turkish carpets to Northern Europe.
If you can buy these for good prices (till 110-115%), can sell for 2-3k profit per item in Northern Europe.
The problem is that sailing to Beirut from Amsterdam takes a lot of time, Caribbean is a better choice imo.
Long distance trade
One word - India :)
The ultimate trade route, takes ages, but profit is too attractive to resist.
When sailing to India, you can earn around 1-1.5m with Europe->India trip.
When going back, the profits are insane.
For example sold Ruby/Sapphire for 15k ea in Antwerp yesterday. Can buy these for 3-5k in Ceylon.
Other great goods: Cat's eye, Cinnamon, Cardamom, Pepper, Aventurine.
Gem trading is very helpful, also spice trading would help too.
Need lots of fame to get permits though.