"I just finished a textbook on New Testament Greek and am honing my linguistic skills. I'd appreciate any advice you may have to offer." -- R. Jones
My advice is always to get some accountability – the only way to learn a language short of full immersion – which in the case of ancient Greek is impossible. For accountability, I would sign up as a credit (not audit) student at a university or seminary. Plan to take at least 4 semesters of Greek—6 would be better.
Then stay fresh by doing a little translation work regularly – at least once a month, though ideally every day, from then on. If you love the New Testament you will have a strong motivation to improve continually.
Hope that helps.