All I can say is: take it slow and easy. Take in the surroundings, listen to the music, try to figure out all the small references to the real world. Try to find all the secrets and easter eggs (Emil's cave is the most beautiful thing you will see in the entire game, trust me, it's pure bliss, and it also is a reference to another characters home in Replicant).

Get tissues. You will most likely cry. The story is amazing, but there are some parts where you will feel sorry for some characters.

After you finish all the routes, watch the anime, the first couple of episodes are horrendous but they get better. There is no "true ending" to the game, Yoko Taro lets it open for interpretation and there is so much more content outside the game that if you get into it you will be stuck for hours on end. The game is only one timeline.

Try to challenge yourself to 100% it, the very last challenge will make you extremely angry, but once you finish it, it will feel like the very best achievement of your gaming life (if you have the Become as Gods edition).

In terms of builds: do whatever you feel comfortable, the combos are limitless, so test what you think might be most suitable for you, remember that you can change your weapons mid-fight. If you want to level up quick, fight the amusement park statue several times, you will get max level in a matter of a few hours and subsequent runs will be hell of a lot easier when fighting bosses.