All said is good. However, sometimes you don't fight the enemy in the open (or head on) to beat 'em. Noone has suggested avoiding some fleets then rush to attack their outlying colonies and damage the infrastructure. Just make sure you have a few good W-Platforms.
Many times that puts them in a position of overextending their supplies. You attack and destroy their RD's and SY's on their borders. Ships that run out of supplies are generally easy pickin's
Also, getting a few outlying systems to riot can cripple their economy.
Many times a good counterstrike can be better than good defense...Just IMO...