Every time you will reach new rank - your investor Mrs. Lydiya will sign some sneacky contracts for you, so you must be prepeared to make them quick.
This Guide from ptmadman12 will help you find ports with goods you needed.)
And don't forget to save before you will start this contracts, anything can happend.)

1. Big Contract For Hamburg
First you will get Consignor Rank, I very advise you to have 3 fully upgrated Bulky 120/20.
Because they make your life much easier and faster, and you will need them during all game.
(You can even berth them somewhere in Havana, for example, and let them there waiting for new small but important tasks.)
When you reach Consignor Rank, you Will get "Big Contract For Hamburg".
You will need deliver to Hamburg: 200 TEU of Timber, 500 TEU of Metal, 350 TEU of Machinery, 150 TEU of Electronics, 50 TEU of Furniture.

2. Coffee for Russia

Here is a Ship list from Emily, but I give you my little hints.)
Little hints: a).repair ships to keep your fleet in good condition >90% or atleast >80%.
b).-then you buy ship, first - fully repair it and make all improvements, only then use it.
Inmportant notice - you can repair ship with only 10% (use slider) - it saves time! No need to repair from 85% to 100% - it will took 8 days, make it 85% to 95% - it will take only 4 days!)

1. Feeder Class
Buy, fully upgrade and keep three Bulky 120/20 - you will need them in many future contracts.
Condition drops less then 1% per trip. You can repair them then their condition drops to 90%.
2. Panamax Class
Best ship here - Super-Speed S. He is second largest Panamax, but he is fastest, and it's totally compensate he's second place!)
3. Post-Panamax
Super-Speed W. Biggest capacity, high speed and longest trip.
4. New-Panamax
Super-Speed S-Scale - also biggest capacity, high speed long trip.
5. ULCV
Bulky Half-Size - I think he have most balanced efficiency ratings.

Best ship in game, on my opinion, is Super-Speed S-Scale.
He is big enough, fastest of all (30 knots at full speed), beautiest and he can use Panama canal!

1. Titanic
There is a "Titanic" achivement in game - you must christen ship as Titanic and let him sunk.
It's easy.) At start of the game, you have one not new Starter Feeder Class ship - just name it Titanic and do not repear it. You will save your time and money for first time, and will have possibility to get What a piece of junk! (when you need to berth in a port with less than 5% Condition) achivement also! :D
Note 1: What a piece of junk can be reached only on Easy, because then ships sinks at 1%, Normal 20%, Hard 40%.
Note 2: When his condition drops less 5% - do not take any contracts for him, because he can sunk with cargo and you will get penalty and loose reputation. Make him travel empty, because when he stand at port - he will not loose condition and will not sunk.)
Note 3: If Titanic will trap in storm or reefs - do not sail round, sail trough - it will drop condition faster. Also do this then it have fire on board.)

2. Cast off
It is unnessesary to turn arond ship when you cast off. If driving back will be faster and easier - you can rich "World line" shipping backwords.)

3. Before you get next rank - complete all your affairs, because once you get a new rank - you will receive a new nasty contract from your investor. You will need all your ships to complete it in the allotted time. And don't forget to save game then you start proceed this contract.)

4. 10x manual dock or cast
When you reach Magnate rank, you will have new task - manually dock or cast off 10 times, 2 times per each type of ships. If Feeders and Panamax will be easy for you, Post-Panamax and New-Panamax make you swet, so you need to do it in easiest ports - Dakar, Salalah, Lagos and Georgia Ports.)

5. Subsidiaries.
Buy Subsidiaries on all 5 continents - it will give you greater range of ships and you will get Continental Drift achivement also.) You can make only 5 subsidiares, but once you visit port - you can easily get there without casting there ship and establish or shut down it.)
So you can easily get Start Small achivement, make it in some small port for Feeders only.

6. Repair
If you miss 90% condition and have 89% - no need to wait all 8 days for repair, just place slider to 99% (or other +10%).

7. Finish lane on Hard
When you play on Hard, reach Tycoon level and offer to buyout your company - not rush to buy ULCV ships. First - they increase your company value and you will need more money to buyout. Second - they not so efficient compare to New Panamax Super-Speed S-Scale. They slow and you can load them more then 80% not so often.

1. Fuel prices, speed and fuel consumption.
If you play at Easy - there is no rule where to fuel up and how much it cost, beacause you earning so big what you can affort whatever you want. :D
If things will change at Normal and Hard - I will let you know.)
UPD No problems with fuel on Hard game also, so don't let it bothering you.)
However, useful to have the habit - always fill up when you enter the port. First fuel, then contracts.

2. Illegal cargo and contrafaction
If you transport some goods what needs some specific tools on your ship (like Refrigeration Systems or Freight Insulation) but they are missed and Inspection will check your ship - you will get penalty and loose some reputation (nothing crucial, but bites).
Questionable goods have afforable prices, but if get caught - fines will be big, and for your reputation also.

I advise you get achivement on easy game.) 35 of 38 I made in 56 hours of playing.)
1. Whale Watcher
Catch Sight Of A Whale. I think whales can be in any port, but you can see them only if you docking manualy.
2. What a piece of junk!
Berth in a port with less than 5% Condition. You can get it only on Easy game.
3. The Blue Riband
Do the New York – Dublin crossing in 8 days or less. Just travek from NY to Dublin even without cargo.
4. Iceberg, right ahead!
Christen a ship "Titanic" and sink it. You can rename any ship. Ship will sunk: on Easy - if he wiil have less then 2% Condition, Normal - <20%, Hard <40%.
5. Breadwinner
Take Foodstuffs from your home port or your subsidiary to all 55 ports. You need to deliver only(!) Foodstuffs to all(!) 55 ports, including(!) your home port and subsidiaries. And some of the ports you can't reach from one. For example my HQ is Valencia - 51 port was reached from there, but Anchorage, Vladivostok, Honolulu and Valencia was avaible only from Melbourne. And remember - not all ports have Foodstufs.)
6. No Stranger To Danger
Experience all three random events on one journey and survive them all. Just park all your vessels, take 1-3 Feeders, put them at minimal speed 5 knots and give them longest deliveries (it will be 60-80 days). Put game speed x2, seat and wait, when some ship finish delivery - give him another long trip, and again and again. Vessel must berth in a port to get achivement. If you lucky - you will get it in one evening, I get it on third.) But don't foget about docking fees!!!

It is simply. Do not take it.) You can make money on your own easily.)
As they say, "If you can pay the interest on the loan - why do you take credit anyway!?" :D

But there is one thing where loans can be useful - when you missed investors payoff and your account sadenly going in big minus ( -$30-50 millions). You can not repair ships (not a big problem), Automaticly dock and cast off (fixable) and biggest issue - can't refuel.
If you have -$30 mln - you can take $50 mln loan and pay it out in 1 month. No need to hold it forever.) It can happend on Hard level of game.)

1. First subsidiaries
Establish your first subsidiary at biggest ports, because first is for free.) Second - in Rekjavik, because it will cost only 500 000, and you will have more chances to get brand new Bulky 120/20 (because you need them 3).) Later you can change subsidiary port without visiting.)

2. Buy biggest avaible ship.
It allways be Light Carrier F! :D No matter what condition he have, you will not upgrade or repair him, he will work for sale or sunk while you will not have your first brand new and fully upgraded Bulky 120/20. You can repair him if needed at 10% per time only to keep him in buissnes.

3. Dock and cast off manually.
First - it saves you alot of money at start of the game, second - it will help you to get some achivements, third - it's easy to do on Feeders! :D

Feeders
Bulky 120/20 - somewere about . They can ship long time until drops 1% (from 100% to 99%), 1 maximum distance trip at full speed.
Panamax
Super-Speed S - approx. 5 days trip per 1 % condition at 26 knots.
Post-Panamax
Super-Speed W - approx. days trip per 1 % condition at 28 knots.
New-Panamax
Super-Speed S-Scale - approx. 4 days trip per 1% condition at 30 knots.
ULCV
Bulky Half-Size - approx. days trip per 1 % condition at 23 knots.