This is awfully rough and done last minute, but I'll update it as I go along and answer questions. But to provide some basic ideas, I'll pitch some stuff to get novices started with training.

rundown for basic playstyle:
use hot stuff to cool down, cold stuff to heat up. Reactive (purple) makes explosions when hot and makes icicles when cold.
Major moves are: "Draw/Expel heat" "Ice Armor" "bolt" and "mist"
the bare minimum needed to play a Metatherm. Keep those at close at hand and close at mind.

TOP priority is to COOL DOWN (by using hot moves) and ARMOR UP!
KEEP YOUR ARMOR UP!!!
Keep it up.
Otherwise, you will never get the chance to setup properly.
Once you're armored, you can properly pressure.
And your off. From there you can lab about and COMBINE PROJECTILES/MELEE to cause THERMAL REACTIONS.

Example exercise:
Try hitting a "Mist/bolt 0" with a hot attack, be it a projectile or a melee strike. Easiest method is EXPEL HEAT
now do the same with a cold attack!
then try the opposite for each ("react" a hot or cold cloud/projectile)

If you're running too hot/cold, click the "Heat/Cold Death" super ability to immediately (and violently) equalize your temperature.

Anyhow, hopefully that wasn't too overwhelming. But for more advanced info, I'll espouse particularities henceforth.

THERMAL BASICS:
Purple = "reactive/conductive/neutral" (Think of it like super gasoline that explodes when HOT, or snap freezes into icicles when COLD)

Orange = "hot" (High damage moves/upwards movement. Very offense/movement oriented and involves exploding when CONDUCTED or forming wind/vortices when COLD.)

Blue = "cold" (Safe/Defensive moves, either featuring armor or long lasting projectile hazards which get bigger when CONDUCTED or radial airblasts when HOT)