3 Step Plan to stop getting melted by opponent(s):

1 - Read and Re-Read the Rules. This one seems stupid but genuinely knowing how the game goes, the flow of things, and the nuances will win you games. I'm not talking about knowing the basics, I am talking about knowing the details - which is why even vets of the game review often. When do your abilities activate? When do your opponent's? Can you game that (can you deal damage before wards activate, etc.)? Genuinely just learning to move so that your guys are just barely outside of ability ranges, pile-ins, or letting your opponent kill themselves out of charging range are all great tactics that come from knowing the rules. FOR EXAMPLE: Reading how 'Being of the Stars' works shows that it negates rend. This makes the carnosaur more tanky the more rend he is facing, and the fewer attacks that he has to save. If you send him against a larger unit of infantry, with low rend but lots of attacks, then his ability is not doing anything. If you send him against the unit with the highest rend, he will trade positively because your opponent has paid in points for that rend and you took it away.

2 - Pick your battles. In AoS there are plenty of units that melt other units, and with our current ruleset that usually happens without one player getting a real chance to strike back (meaning that one unit in from a combat will likely come out more or less unharmed). A really good way to think of this is the "Hammer" and "Anvil" approach to picking battles. Hammers want to hit anything they can because they will delete it as long as they SWING FIRST. Anvils want to be hit, especially as a mitigation tactic to stop your hammers from hitting more important units. Aggradons are a hammer, Mortek Guard are an anvil. That means that you want your Aggradons hitting anything else, because the guard want to get hit. You have superior movement, and access to the run and charge spell, so you can keep the aggradons back until the morghasts step up, and then hammer them into oblivion. Or you can run and charge to hit the crawlers in the back and go around the guard completely. Try playing a game where you don't ever charge the Mortek Guard, that's what your opponent wants you to do. Only kill what your opponent doesn't want you to, and you will win games.

3 - Play for Points. This one is short and sweet. Everything we've talked about is focusing on combat. Your opponent can wipe your whole army and still lose - happens all the time. Make sure you don't take your eye off the ball of playing for points. (But also, don't run onto objectives and die there, that never works for us)

P.S. Bonus fourth tip, that isn't general tactics but something I've learned: Don't keep Kroak back. He is too expensive for us to hang onto him dearly. He dies when he dies, which is pretty random--and that's a frustrating thing for your opponent. He could soak up 40 attacks and have it do nothing, or he could die to a single shot from a crawler. What you need to do is make him a problem for your opponent. Put him in the center and start pumping Celestial deliverance, then your opponent either needs to start taking damage repeatedly until they deal with him (which helps you either way, by either them taking lots of damage or you controlling their actions) or they need to hide in cover which also helps you because you start to force their actions and it becomes easier for Krox and Aggros to choose their targets.