We have a modal in our app where people can search for products within various user flows (in this instance it's for connect products in your inventory to your Amazon listings, so you can keep orders etc in sync).
It needs a bit of an overhaul, so far I've improved things like moving labels above fields, more meaningful labels, aligning fields, some style changes.
I've attached the mockup so far (feel there's more room for improvement). The trickiest part is getting the 5 fields to work within the space of the modal (moving this out of the modal or changing the modal significantly would be out of scope). The space above and below the search form changes depending on the user journey, so will have to be careful about changing that too much.
Here's a new mockup:
Here's a another new mockup based on the answers posted: