What's the most important thing to learn as an MMA novice? Blocks?

An MMA novice? Well if you are a striker, practicing Take down defense would help in MMA, then mastering a ground game if your TDD fails in keeping you vertical.

if you are a complete novice with no combat experience, I’d say master your striking, use all your limbs, then master grappling.

 

Yeah, it would be helpful to know what is meant by novice, whether that means total novice to all combat sports, or a novice to MMA itself, but with at least a background in 1 or more combat sports.

Mastering escapes from side control are awfully important if you ask me. Escaping side control is to beginning grapplers/mma fighters what acne is to teenagers: a source of constant anxiety. The good news is, by the time you get to purple belt, or even middle blue belt, you discover that getting out of side control is pretty simple, even against larger opponents.

A well-schooled grappler can reverse from side-control, they can recover full guard while threatening submissions, they can work to butterfly and angle for sweeps, or they can get to half-guard and pick between back-takes or sweeps.

It's hard to pick any one skill or discipline as THE most important, but its easy to predict that a fighter without side control escapes has a bleak future.