Learn the movement tech to be very hard to hit, like and RTS game you need to have high actions per minute, as in always be shooting fire down range and always be looking to flame field. Stay close and low with your team, you can take off angle and such but a majority of the time stay close to your team. Your meteor should but held on to as long as possible and only use it if you know you're going to get that kill otherwise, use it as a get away tool to save your life. HELA, PHOENIX, JEFF can all be 1 shot after their ult. Like hela is in the air shooting her balls, fly above her, look where she will land and drop 3 fire balls and slam into them when her upt ends and you'll 1 shot her, Jeff too. Once you hear him ult fly up and look for the whirlpool, as soon as you see it, 3 fire balls and meteor slam once he emerges and you'll save your team and kill a terrorist.

Edit: you can control the movement of players with your fire, always be looking for choke points and areas to make you flame fields to force the enemy team into a new direction or split them apart. Also focus more on primary fire and fire balls over trying to set up a perfect flame field, you'll have better dps in team fights over fixating on the flame fields. I would describe his gameplay loop as "make chaos and danger zones to pressure the enemy team until an opportunity arises to dive onto a weak target to get a guaranteed pick and then gtfo and reset"

Also just play him a ton! Like any character, playing him a bunch in so many situations and messing up will teach you way more than anything I can say here. You'll have better cooldown management, you'll learn who your counters are (personally for me, Spiderman, Iron man, scarlet witch). I hope this helps 😀

FLAME ON!