The boring answer is that there is no quick fix, but it will become easier as your technique becomes more efficient and you become more coordinated, so that easy, even movements happen automatically.
Some things that may help though:
If it's a repeated sequence of sixteenths like so
g-a-g-a g-a-g-a g-a-g-a g-a-g-a
You can use a fingering like
3-1-2-1 3-1-2-1 3-1-2-1 3-1-2-1
to provide a bit of structure. Let your hand move slightly as it needs to to accomodate the fingering. You're then making a larger gesture for each group of four notes, instead of repeating a smaller gesture over and over.
Also, slightly accent the first note in each group of four, to mark the beat, and feel the beat in your body at the same time.
Finally, practice slowly and make the groups feel like so:
A g-a-g-A g-a-g-A g-a-g-A g-a-g-A
Where the capital A is the beat, and the lower case letters are played in such a way that they feel like they provide direction, propelling you towards the next A (almost like a small crescendo towards each A). You can do this in a rhythm where the A is longer and the lower case letters quicker, but you should also do this slowly with a perfectly even rhythm, while still keeping the feeling that the three lower case letters provide direction towards the next A.
Let me know if any of this helps.