The X3 series is very complex and it can take many hours to gain any significant understanding of the game's mechanics.
At it's core, it's a space trading game. You want to buy items at places where they are inexpensive, and sell them at places where you can make a profit. For instance, buy Energy Cells from a Solar Plant, and sell them at a factory or other station that requires them.
Doing this manually takes quite a bit of time and effort, but eventually you'll gain the funds and resources required to command additional ships - you can then send them to run these hauling operations for you, earning you cash while you pursue other things.
Eventually you'll get enough money to build your own stations, and then you can make mega profits producing finished goods directly from raw materials. Then your job becomes one mostly of macro-managing the production chains to ensure that the money continues to flow.
Mining is not something I engaged in much personally, as it tends to require some large ships and a lot of manual effort. Combat's kind of an advanced subject, as you'll likely have to sink a fair number of credits into a good "dogfighting" ship and the appropriate armaments for it.
If you're having trouble with a specific mission class, you might browse the mission guides on the X3 Wiki, which contains information about how to complete each type of mission, and what you'll need in order to be successful.
To point you in the right direction for a more in-depth guide, check out the X3 Handbook - it's a collection of a number of useful guides generated by the community over the years. Sometimes the tone is a bit on the "conversational" side for my taste, but it's still chock full of good resources. There's an emphasis on the Terran Conflict (TC) content in some of the early chapters which you may wish to skip over if you're starting with Albion Prelude.