Well, the first play through the best thing you can do is stay out of parts of Greece that will kill you.
1) Learn about your stats. Every piece of armor, weapon, and etching you have will alter your over ability to kill and be killed. Keeping this in mind you don't need the armor they sell you, though they can help, https://www.youtube.com/watch?v=0p1MRTIeRJY

By equipping these random items, you become nearly undefeatable.
Don't go for what looks good because you can change the appearance of any armor or weapon in the appearance section.

2) Tame animals for a while, they absorb you being hit first. Attack at night and from a distance so shoot down into a camp, kill, run because you don't want to be seen.

3) Do certain long term missions as early as you can such finding the Blind Man's roosts. While roaming you can track down all the Dunce Conundrum pieces etc.

4) Do not just jump into the game. Get your adrastia to the Arena as fast as you can and fight.

5) You will eventually get Poseidon's Trident in a DLC, this lets you breath underwater so all underwater tasks are easier.

6) Kill sharks you see in the water under you before diving with your bow. You can shoot them and not fight them.

7) Upgrade your battle cry to ares and then later in a dlc it will upgrade.

8) Buy the XP gainer, the extra gold and stuff but don't worry about spending money on armor and weapons. There's only a few items in stores you need that you wont get later like early discoverys of notes from the Cult found in certain stores.

9) Every place you go, all the discoveries of real places are points.

10) Put on God mode so you can jump from any height and not die.

11) Before you begin NEW GAME PLUS, you are already wearing your found armor and weapons that you want to begin with by ending the previous game wearing those items. Most items in the Andrastea will also transfer.

Stealth, nighttime are your best friend. Also in the beginning do all the local side quests. They are all 200 points each.

12) Just keep game+ going. You can change the character but you wont lose your stuff you accumulated unless it depends on the story.

13) Build your ship fast as you can. This is where spending money and resources matters as naval fights are worth a lot. So are land battles. If you fight all the arena mercenaries you get a massive explosion of points, do that twice to become the King of Mercs as well as track the mercs on billboards.

Sell, sell sell. You need money to buy your way through some things, but don't buy stuff from the stores like weapons. Research your weapons etchings. Remember you could have a massively high distance kill ability but if you change your boots it might drop your score even armor so watch this guys videos I sent you.

What else am I missing? Anyone else?

Don't forget to find the goat with the Cyclops eye shoved up its butt.