Here is some tips if you want:
The first priority in high difficulties is to produce ~3 energy per discard turn 2, or 4+ per turn turn 1. ~2 per discard work if you are desesperate. That mean that your first stack is extremely valuable because if you draw a power grid turn 2, you usually want for it to be available*.
*I still personnally play a draw 8 wind or solar turn 1 above it, but that's the only exception.
The second priority is to do something useful in all stacks. That can be -1 emission per turn (+1 tree, -1 symbol every turn, -2 symbols&+2energy needed), that can be +1 draw per turn (or a card with a conditionnal draw which draw 5+), that can be +2 (or +1) resilience per turn.
Once you have that, you want to reduce the emissions done per turn to less than half it's initial value, so at two players that start at 20, you want it at 10 or below.
After that, you want to increase your resilience/greed more/reduces communities in crisis/do more short term plays (like using 3 cards for a temporary -10~-20 emission). It can be summarised by try to not lose immediately.
After that, you have everything under control, and can do whatever is remeaning (reaching drawdown, doing challenges, remove communities in crisis, cover draw to defend someone which could be losing,...).
Often in lower difficulties (and sometimes in high one) you can skip the middle part because you will already be in an extremely good spot.
Lastly, pay attention to the energy you produce in the thermometer. Every 5*number of players energy added crisis will deal one more damage and you will roll one more dice [unless that dice roll cloud: 1/6]. So turn 1, you really want for one player to do at least -1 emission, and later on, you can plan your turn to end exactly one below the next threshold.
.
Don't be afraid to keep a stack with only two cards which do something useful the whole game.
You usually want to play cards above a stack for immediate value, do something with it, and then cover it again, and again. You will usually have one stack much bigger than others, but that will open to you a lot of synergies every turn.
Alternatively, you can have a stack with 6 cards and a draw 3 that you can keep during some turn.
Often you should end a stack with a great card that you want to use this and next turn. It can be -3 factories, it can be +2/+3 draw. Then the following turn, you have the choic of keeping it one extra turn, or covering it and use all the symbols that stack already have.
The main thing to understand is that your priorities change drastiquely depending of how well the game is. At the start, discarding one card for any effect is usually bad: that cost you a big ressource. But once you reduces the emissions done, playing defensively increase in value and so doing that same play is fine. And once you got the game under control, if missing that effect can cost you the game (like missing a resilience), that become a great play.
Per example, there is a solar energy card which can be used a number of time equal to the social symbol you got on that stack and which add an infrastructure resilience. It already happen that in late game, I put 3 social on that stack and discard 3 cards just to get +3 infrastructure. That's normally an extremely bad play, but as I said, if you have way too much communities in crisis so are close to losing, and you got the game under control (you got like -5 emission per turn), and your others resiliences are good, then now that's the play to avoid losing.
The first few games, it can feel really hard to manage everything. I got frustrated too. But eventually, it just clicks, and you figure out what to prioritize. Now, even with challenge cards, it often feels too easy. ;D
