Get resupply stations, interceptors, blastboats, Vindicators. Then focus on economy until you've researched at least level 1 in thin ranks or whatever it is that give you free (no upkeep cost) supply & command. At that point, you'll have the largest fleet, although probably fewest caps (don't worry, this will never change, the PA more than anyone else relies upon the frigate & cruiser) since you only have ISD-I's.
Once you've got the free supply & command, your Star Galleons, Acclamators, Venators, Procusators, and other capital ships. PA is unique in that they're the only faction that can COMPLETELY abandon one of their capital ships. Once you have ISD-II & Secutors, the ISD-I offers no good reason to EVER build. The Secutor can colonize, the ISD-II can do overwhelm & tractor beams. Unless you really care about the probe droids ability that you need to be fairly high level to take, then the ISD-I becomes redundant and useless.
ALWAYS have at least 1 Praetor. You'll need it to be a damage sink to allow your fairly weak cruisers to survive and thrive. The bulk of your fleet should be Secutors. Damage on par with the ISD-II, but able to colonize, improve your fighters abilities, and carries at higher levels a LOT of fighters (7 squadrons @ 8th level). ISD-II rounds it out, with a Dominator or 2 for when you really don't want the enemy to get away.
Always build corporate command center and upgrade all 3 properties on your Capitals. ESPECIALLY Praetors...they're sluggishness is only SLIGHLTY offset by this, but it helps a ton nevertheless.
Procursators & VSD's (until they're replaced) should be the bulk of your fleet. Procursators are incredibly powerful cruisers, although you do pay for it. Venators are great for tehir money. After all the upgrade, do over 100 average TL dps while carrying 3 squadrons, and having upper 2000's hull & shields. They're the things the Praetor is there to protect. 2 Skiprays + 1 Interceptor per Venator is a dangerous combination.
Unlike the NR & IR, your beginning cruiser never becomes useless. Because the Gladiator can carry a blastboat, it's still useful until the very end.