The AI is dumb. Make ships, lots of ships. go kill the ais.
Seriously that is the way. And you know the ai's are going to gang up on you if it is ffa unlocked so try and find choice planets for tactical structures and frigate factorys, send in frigates passed the front of the ai to mess with the ai's economy, use cap ships to bomb planets to attract ai fleets to the defence then run (position the cap ship so it can flee in the direction you want). Always be attacking. DO Not lose the planets where you have your frigate factories. Consider putting most of them 1 planet behind the front lines, keep you milstations deep in your territory
There are lots of viable strategies, Keep your fleet at #2 or #3 to have a slightly better economy than #1 and replace your loses asap.
At the start all ai's are enemies, raid them all if possible with small sacrificial fleets, do not expect them to come back just keep them moving deeper into the enemy teritory looking for trade ships and structures easy to kill on raiders path and avoid fighting ships that shoot back ( the ai will waste money on hangers and point defenses so watch out for these, especially the hangers). Then start to chose which ai you want to accept missions from. Do not sign trade alliances with AIs that are not right next to you as you trade ships will suffer attacks as they go through enemy territory. Although sometimes you can sign trade alliance with every one but this is risky.
The ai is really dumb, you can park a carrier in a gasgiant and kill trade ships, the ai will take a while to react, it may never react.
Keep building the metal only frigates - while using the crystal for the high tech ships and research- for raiding behind the lines but distract the guarding fleets with serious fients so that the low tier frigate can get through when phase inhipitors are built.