Five basic things that I want in season four:
1): An episode with none of the mane six in it.
Here's why: I know the mane six are the stars, but perhaps in one episode there could be a focus on some new or nobody characters. It would be pretty cool. We need episodes that have nothing to do with: the Cutie Mark Crusaders, the mane six and Spike for a change. Perhaps season four could allow this.
2.): The return of Twist.
To put it simply... I like Twist. She barely got any screentime and I wish for her to return. In season four I do hope that she gets her own episode dedicated to her life or perhaps trying to win back Apple Bloom's friendship. I don't know, it just seems pretty plausible for her to return in season four.
3): A new type of pony: Sea Ponies.
I know, Sea Ponies aren't new. But they should get a comeback. It would be pretty cool if they brought them back but I doubt they will. It could happen. I mean we got Crystal Ponies which are pretty awesome, but I want Sea Ponies to get their debut. Perhaps now would be a good time to introduce them. I don't know if they will be introduced but perhaps they could be.
4.) An episode involving jealousy.
It's probably too late now since Twilight is a regal princess, but I always wanted to see an episode where Twilight makes a new friend and all her friends get jealous. This would have been perfect for season one or season two but it never happened. By season three I lost hope. Perhaps this could happen with the Cute Mark Crusaders instead but then again...it might be too late for that, too.
5.) More information on Princess Celestia herself: an episode dedicated to her.
We don't know much about Princess Celestia's life. We know she's a princess, but she needs an epiosode for herself. Perhaps it would give her a background: how she became a princess, when she earned her cutie mark and much more. All we know is that she's a princess and teacher to Twilight Sparkle. Nothing more. It would be great if an episode for her was in season four and I would be excited to no end if it were to come true.
And these are just some of my wants. I want a lot more but I can't think of anyhting else.