X3:TC Lessons Learned

Wish I'd known about the game sooner
The game is deep and immensely satisfying, and I wish I'd know about it sooner! At first, I was afraid I made a mistake in buying it because it seemed hopelessly complicated. But I watched some of CmrDave's tutorial videos, then started to discover parts of the game on my own, and eventually found it staggeringly fun. I can also play it like a simulation game and choose to leave it running, letting my empire take care of itself while I sleep or go on a date with the wife.

Download the Bonus Pack
The bonus pack is signed by the X3 developer, Egosoft, so it does not mark your game as modified. It adds some amazing functionality, and I wouldn't play X3 without it. (I tried at first, and I regretted it!) I'll just briefly mention the CLS/CAGs in the Bonus Pack below:

CLS1 = the Trade -> "Start internal commodity logistics" command, from the Commodity Logistics Mk1 software
CLS2 = the Trade -> "Start external commodity logistics" command, from the Commodity Logistics Mk2 software
CAG = the Trade -> "Start commercial representation" command

Like everything in the X3, these take some experimentation to setup just right, but their functionality is game-changing. I use CLS2 extensively for resupply and one-off deliveries. I use CAGs for most of my money-making and station/complex maintenance.

Setup stations early
I thought UTs were great when I first started using them, but little did I know that stations/complexes with CAGs are even better! Complexes in high-sec space are solid and safe money-makers, and you can totally set and forget them (with a CAG or CLS freighter). They make great storage dumps for energy or other resources they consume. You can add stations onto a complex later, and deactivate individual stations. Thus you can repurpose your station over time. Complexes are valuable in many dimensions (e.g. docking, resupply from excess resources), not just for profit. I don't use STs/UTs at all now.

Start training marines early
Even if you don't do much ship capturing, you need marines for some plots and special ships. Marine training takes ages, so start early. Every time you find a station with marines, look for any that have 3+ stars in fighting, buy them, and start them training. Everything but fighting is trainable, so the only important factor for purchasing them is fighting. Keep training them until they are 5 stars in everything else. Eventually, you will need them. I would recommend collecting up to 20 5-star marines over time. This happens to be the amount an M7M holds.

Put complex hubs near gates
This makes it quick for CAGs and resupply ships to dock at the complex. My first complex was built 150km+ from the nearest gate to avoid pirate traffic, and I had to assign it a lot of extra CAGs because each ship was spending more time flying to it than making me money. And then the game spawns pirates to attack your station anyway if you use afk SETA.

Notice that I said "near" gates, not on top of gates. And notice that I said the complex hub, which you can place a little bit away from the stations. With the latest (huge) stations that I build, I have the hub within 20-25km of the gate, but the bulk of the stations are out of the field of normal view. I do this by placing 10 or 20 of the stations pretty far apart and in a line going up out of view. Then the rest of the stations are layered above that. This is a more advanced technique that takes some practice, because the complex hubs don't always get placed where you tell them. So make sure you save before you start!