Hi Richard, wellcome!
Despite his apparent simplicity, Mozart is not easy to play.At least, to play well.
This first mouvement is made with scales, harps and trills.
In Mozart, the scales are suposed to be played "detache". Try to play them slow and gradually increase the spead.
One way to gain spead in scales is the parallell sets, described by Mr. Shuan Chang in his book "the piano practice". You may download it, free, in the Net.
But, with PS, we gain speed but not eveness. When I was young, I used to play the scales like this: 1231 (cdef) 10 times; 12312 (cdefg) 10 times; 1231234 (cdefgab) 10 times; and so on... Here, we can try to play fast.
In order to gain the "detache", you may wish to play the scales finger stacato or finger non legato.
The ties: when you play the last note in the tie, you must lift your wrist when leaving the key. You have a video of Graham Fisch in youtube, showing how to do this. The same with Ilinca Vartic; she has some vídeos not paid where she explains this mouvement of the wrist.
Trills: the same as scales - PS: first, you play 2 fingers same time; then, you lift a little one of the fingers and let them fall into the 2 keys; then, the same with the other finger; many times.
Then, 1-2-1 very fast (many times); 1-2-1-2; 2-1-2-1; 1-2-1-2-1-2, 2-1-2-1-2-1 and so on. For thrill eveness, you may play CDC/DCD/CDC....(triads) increasing speed gradually... Trills with 4-5 fingers ou even 3-4 fingers are not very easy. When possible, try 1-3, 1-4 or 2-4. Trills with 2-3 are possible but the lenght of theese two fingers is different and there`s a natural tendency to make the trill uneven.
I must apologize my English, because I`m portuguese, not a native.
I hope this may help you.
Best wishes
Rui