Radiant Backguard
There aren’t really any tips other than to do every achievement you have access to. Anytime new achievements are added, do them as soon as possible because they might only be available temporarily.
Make sure you get your 10AP from dailies every day that you can. It might feel inconsequential in the face of a 39k goal, but the players currently at the top of the leaderboard with 32k will have just under half of their AP from their dailies.
Stitch highlights an important point: no one has got 39K yet, years after the AP rewards system was introduced. So while it is a fine goal, be aware that you will be investing years into reaching it.
It is impossible to have more than 32800ish AP at the moment, even if you played from start and did the impossible ones like 10k pvp wins. Ask again in 2-3 expansions time.
1st person worldwide to reach 35,000 achievement points.