1
Treat the first guess as a purchase
You are spending a turn to buy information. The best opening buys the most: five different letters, all common ones. You will almost never win on it, and trying to is how people waste the most valuable turn they have.
2
Grey Is Information Too
A guess that comes back entirely grey feels like a disaster and is often the most useful turn of the game — five letters eliminated at once. What loses games is refusing to spend a turn that cannot win.
3
Move amber letters, do not shuffle them
Amber means the letter is in the word and NOT in that position. Putting it back in the same slot guarantees the same amber and buys nothing. Move it somewhere it has not been.
4
Watch for the Shared-Ending Trap
Four letters placed and one blank is the worst position on the board when the blank has six candidates — _IGHT gives you EIGHT, FIGHT, LIGHT, MIGHT, NIGHT, RIGHT, SIGHT and TIGHT. Spend a turn testing several of those letters at once rather than guessing them one at a time.
5
Longer is not just harder, it is different
Past seven letters the game changes character. There are more places for a letter to hide, so eliminating becomes worth more than placing, and confirming an ending like ING or TION can settle several tiles in one turn.
6
Remember that a letter can appear twice
It is the rule that catches everyone. The board marks a letter only as many times as the answer holds it, so a second E can come back grey while the first sits blue — that means "no more of these", not "not in the word".