mining does get extremely boring quickly
mission running is lucrative, just not at first.
gouging the market is also good. I used to put in purchase orders for things (i only dealt with ships costing 20M plus) id put in buy orders at 10% of market price in hopes that people got confused with number of 0's (not sure if its as easy to do that now) and resell at 80 -90% current market, sometimes id even take 2 0's of and get it at 1% on very expensive items. Made my way to 2B that way. That was more a waiting game yet more lucrative when it paid off, i got some fantastic ships doing that, faction battleships etc.