I find mixing up what I'm doing is the best way. I do a bit of exploring, then run some missions or do a bit of trading and then there's war zones and bounty hunting as well. I rarely find myself bored, always something to do and if not as has been pointed out go and do something else instead.
I've gone the opposite way.
Enlisted the help of my Son, we are both currently dedicated to mindless monotonous trading.
We are taking it in shifts all the way to Elite.
Next up, exploration to Elite.
Both ranks were second from Elite, but we both know, the last step is worth all the other steps put together.
We hope by that time there will be more interesting and complex missions available, or by the very least, new toys to spend our credits on.