Don't underestimate the importance of battlefield intelligence. Keep scout ships or probes along the perimeter to give you an early warning of when hostiles are coming your way. They will be the first things to die when the shooting starts, so if you can control the start of the war, either pull them in or protect them. Scouts on the perimeter are nice because one can use them as decoys and cause them to be chased around the screen, all while still watching the enemy.
My personal strategy is to have spy ships posted on guard near the important alien systems and to have some other ships to keep track of important resource starbases in case I need to plot a strike on one. Obviously, Eyes of the Universe is a very important wonder for me to build. Being able to see the fools coming from a sector away is far more helpful because I can do it with fewer ships. Just be warned that the Eyes only expand ship and starbase scouting ranges. Planets are still pretty blind.