With small sprites, you should exaggerate the important features. Give the wizard a bigger hat, make the brim much wider. It's okay if it obscures the face more, since there's not much to see there anyway. The purple rim on the robe looks like a shadow that doesn't belong. Perhaps use a lighter rather than darker pattern? You could also add visual interest by giving it a shape other than [rectangular strip]. You could make it wavy or triangular, or you could put a pattern within the strip.
You could give the wizard a belt with trinkets and potions hanging off it, so that he's not just a purple blob. It would be difficult to have all that detail at this size, but just suggesting some colours there and breaking up the purple should work well enough.
The knight has no hip protection. He'd go down with one hit! Hip protection is important because the hips are an easy target, since they're large and don't move around very much. I think hip plates or a metal tunic would be a good addition. Plus, that's something people are used to seeing in knight armour, so it should help the knight read as a knight better.
The knight's chest plate also bugs me a bit. He's got boob plate! Though there definitely was armour that had outlines of the muscles, it was decorative, not meant for situations where the wearer expects to fight. It wasn't armour you'd take to a dungeon. Armour for combat had no nooks on the chest, nothing to catch and direct blows towards the wearer, the shape was designed to deflect
blows. European example
, Japanese example
The floor tiles are in a different perspective from everything else. See how your die's top face isn't a square, but a rectangle? The floor tiles should have the same proportions, since they're also horizontal squares in the same perspective.