Build a couple scouts to take all the resource nodes, build up your metal fast, and don't build up your production. Stick with just the one factory, at most two armories. Most of your resources need to be going into static defenses. Even at the very beginning.
From what I've seen, and I've gotten to where there's half a dozen dreads hitting me at the same time, the only way to survive long term is to get a Sentinel up fast on the east side of the southern entry. You can finish it in time for the first few cruisers, and it will kill them all and hold up long enough for you to get a few more defenses up. Once you've got repair backed Sentinels across the hill, you're solid till they start sending Cronus. At which point things get sticky again.
The last time I played I got my first Prometheus out just in time to get my ass kicked when multiple Cronus took out two thirds of my defenses. If I'd sent it the other direction, instead of engaging the enemy Prometheus that came from the east, it would have been able to kill them and I'd have survived till the next wave at least. Sentinels will kill the other dreadnoughts just fine from on high. It's a bad idea to try and get dreadnoughts too early, might be a bad idea to go for them at all. A large group of Artemis might have taken out the Cronus's vision before it killed the Sentinels, which would have made them come in range and die, and I severely stunted my output when I started building the Prometheus so I was low on cruisers.