I use these terms throughout this guide:

"Main hub": The hub you begin with. If this piece is destroyed, you lose the game.
"Module": Any building, including hubs, anti-airs, towers, etc.

So, what is the first move I make? It depends on the world configuration. If fog is turned off, I always place a dome shield around my main hub. If fog is on, my first move is to place a tower as far away as I feel safe, to give me the most visibility. My very next move, I place the dome shield.
(You can see an example of this opener in the attached image.)

Why is that? The only way for you to lose is to have your main hub destroyed. So taking this seemingly drastic protective measure is actually beneficial in the long run, because it protects your main hub from the majority of attacks. The only way your opponent can access your main hub now is with a crawler (which can easily be disabled before it does any damage), an EMP (which only exposes your Hub for one move), or a spike. Well, or a virus, but I've never even seen an NPC use one of those.

So by protecting your main hub first thing, you give yourself an enormous advantage over NPC opponents. Even Brutakas rarely take any measure to protect their main hubs first thing. This opener almost makes you OP invincible.

Before I tell you the next move I usually make, I'll need to move on to tip 2.

To be honest, I did not think this up myself. I actually picked up this tip from a few youtube gameplay videos. So shoutout to moonbasereplay for this idea.

The tip is this: Before launching a high-cost module, try firing a few bombs or bridges at the same area. Then if you miss, you've only lost 1 energy instead of 7, and you now have an explosion mark to tell you where you just hit.

So as for the remainder of my opener: test-fire a few bombs at the nearest energy pool. Next round, if possible, fire an energy collector at the pool.

(Note: This tip decreases your "accuracy" score at the very end of the game, but it's so worth it.)

Always use a straightedge or ruler to test your firing angle. This tip has saved me more times than I can count. Line up your straightedge with the top of your hub and your aiming mark. Then see where the strightedge extends to see exactly where you are aiming.

Each module has a different level of importance based on its relation to the main hub. This is the case because a destroyed hub will destroy all the modules that were launched from it. It's a cascade effect.
refer to my MS Paint illustration. If module 1 is the main hub, then each cascading module has a lesser importance, because fewer hubs 'depend' on it. So if a tier 3 module is destroyed, only it is destroyed. If the tier 2 module is destroyed, both tier 3 modules go with it. The main hub is always the tier 1 module. If it goes, everything else goes too.

Spikes are my favorite weapon because your attack travels up the chain of importance, not just down. Be careful to remember this when planning your attack. If you take out a tier 2 module, you lose an important link to your opponent's main hub.

This whole thing reminds me of molecular structures for some reason.

(written at publishing time) That's all for now. I will probably think of/remember more tips later on; if so, I will write them in a new section of this guide. Until then, GO AND CONQUER.