I normally progress in weapons and ship sizes so that one ship size = about 1-3 increases in weapon tech. Thus, my personal favorite in the beginning is build the bigger ships at the spaceyards and send my old fleets to take on the newest enemy fleet, usually a loss, but my valiant forces damage the enemy a lot, leaving more current designs to clean up. Wave after wave until I get BattleShip (800kT). Then I will usually have a few captured enemy homeworlds, so half can continue the assult while half gets refitted, and new ships are constructed.
I never really have to worry much about defense fleets. A few ships on a warp point is all I've ever needed (usually hopelessly out-of-date ships too). Probably because I attack the AI at so many points, most of their ships pull back to stop my onslaught
