I would agree with Andrewdwilliams1989 that audio can make or break your work. Bad audio is a dead giveaway of production shortcomings and almost immediately lowers your production value. Shooting with the best cameras and lenses and actors will all be for not if the audio is bad. Audio would be priority number one for me.

My second priority if I was trying to raise the production value of a project would be using good glass. Even if you’re shooting on a smartphone, there are ways to incorporate nicer lenses to raise the profile of your images. And for someone shooting with a DSLR, quality lenses are a must. They are usually pretty cheap to rent, and depending on your shoot schedule/duration, you may be able to shoot with all kinds of fantastic glass you could never possibly own. Def worth considering.

Lighting and production design would be my third and fourth priorities respectively.

In this ‘Naje hierarchy’ of production value, any item is only of value if the items before it are secured. So good production design becomes relevant if you have nice lighting. Nice lighting works if you have decent set up for capturing it. And none of it matters if the sound is bad.

Just my loose rule of thumb…