I've added my ideas to these threads several times before, so I'll see what I can remember this time around.
1. Kreia's Force Ghost, somewhere in the game.
2. Most of the previous main characters having cameos or small roles.
3. Player not being the Exile or Revan.
4. Revan and Exile appearing in-game. Their alignment, gender, and so on being specified by the player in the same manner as with Revan in KOTOR 2.
5. Have a reasonable explanation for why the Jedi Order still exists circa 4,000 years later... as of TSL, there's no way of knowing how they still could, since the entire Jedi Council is dead, and it's not likely that any other masters survived the Purge, taking into account the information given in KOTOR 2.
6. Leave out the following planets:
Α - Dantooine. We've been there twice before. It was different the second time around, but in all likelihood a third time would just be more of the same.
Β - Manaan should not appear anywhere in KOTOR 3 unless it includes the complete and absolute genocide of every Selkath on its surface. And for good measure, all content involving Manaan being cut from the game.
Γ - Tatooine is overused in Star Wars very, very badly. Besides, visiting there again won't give the player anything new to experience.
Δ - Taris. I'm only mentioning it because some people have mentioned it before, so I'll say it out loud: The surface of Taris is destroyed. Everyone
there is dead. There's nothing left except endless piles of wreckage and corpses. Nobody survived. It took the planet millennia to recover, so no big progress will have been made in the years between KOTOR 1 and KOTOR 3.
Ε - Kashyyyk - There's nothing of potential interest there. Just a bunch of big trees. I don't want to revisit the "Wookiees vs Slavers" plot, which by the way, had been used several times in Star Wars before
KOTOR 1 came around.
Ζ - Korriban - Like Dantooine, we've visited it twice before. The first time was good, the second was different and a little disappointing (probably tons of stuff there got cut that none of us will ever hear of), and revisiting it will not give us anything other than what we got with KOTOR 2.
Η - Telos, because any planet associated with Carth Onasi automatically flunks in my book. Serves it right to get the Base Delta Zero treatment from Malak and Saul.
If I can remember anything else later, I'll add it to the thread.
On a side-note...
5: If you want a plot twist, make it a good one. Kreia is EVIL is not a good plot twist, that was obvious after about the third time she opened her mouth.
I didn't know Kreia being evil was supposed to be a plot twist.